DEV: Fix threading error when running jobs immediately in system tests (#19811)

```
class Jobs::DummyDelayedJob < Jobs::Base
  def execute(args = {})
  end
end

RSpec.describe "Jobs.run_immediately!" do
  before { Jobs.run_immediately! }

  it "explodes" do
    current_user = Fabricate(:user)
    Jobs.enqueue_in(1.seconds, :dummy_delayed_job)
    sign_in(current_user)
  end
end
```

The test above will fail with the following error if `ActiveRecord::Base.connection_handler.clear_active_connections!` is called before the configured Capybara server checks out a connection from the connection pool.

```
     ActiveRecord::ActiveRecordError:
       Cannot expire connection, it is owned by a different thread: #<Thread:0x00007f437391df58@puma srv tp 001 /home/tgxworld/.asdf/installs/ruby/3.1.3/lib/ruby/gems/3.1.0/gems/puma-6.0.2/lib/puma/thread_pool.rb:106 sleep_forever>. Current thread: #<Thread:0x00007f437d6cfc60 run>.
```

We're not exactly sure if this is an ActiveRecord bug or not but we've
invested too much time into investigating this problem. Fundamentally,
we also no longer understand why `ActiveRecord::Base.connection_handler.clear_active_connections!` is being called in an ensure block
within `Jobs::Base#perform` which was added in
ceddb6e0da 10 years ago. This
commit moves the logic for running jobs immediately out of the
`Jobs::Base#perform` method into another `Jobs::Base#perform_immediately` method such that
`ActiveRecord::Base.connection_handler.clear_active_connections!` is not
called. This change will only impact the test environment.

app/jobs/base.rb

@@ -197,27 +197,30 @@ module Jobs
       @db_duration || 0
     end
 
+    def perform_immediately(*args)
+      opts = args.extract_options!.with_indifferent_access
+
+      if opts.has_key?(:current_site_id) &&
+           opts[:current_site_id] != RailsMultisite::ConnectionManagement.current_db
+        raise ArgumentError.new(
+                "You can't connect to another database when executing a job synchronously.",
+              )
+      else
+        begin
+          retval = execute(opts)
+        rescue => exc
+          Discourse.handle_job_exception(exc, error_context(opts))
+        end
+
+        retval
+      end
+    end
+
     def perform(*args)
       opts = args.extract_options!.with_indifferent_access
 
       Sidekiq.redis { |r| r.set("last_job_perform_at", Time.now.to_i) } if ::Jobs.run_later?
 
-      if opts.delete(:sync_exec)
-        if opts.has_key?(:current_site_id) &&
-             opts[:current_site_id] != RailsMultisite::ConnectionManagement.current_db
-          raise ArgumentError.new(
-                  "You can't connect to another database when executing a job synchronously.",
-                )
-        else
-          begin
-            retval = execute(opts)
-          rescue => exc
-            Discourse.handle_job_exception(exc, error_context(opts))
-          end
-          return retval
-        end
-      end
-
       dbs =
         if opts[:current_site_id]
           [opts[:current_site_id]]
@@ -334,9 +337,6 @@ module Jobs
 
       DB.after_commit { klass.client_push(hash) }
     else
-      # Otherwise execute the job right away
-      opts["sync_exec"] = true
-
       if Rails.env == "development"
         Scheduler::Defer.later("job") { klass.new.perform(opts) }
       else
@@ -358,7 +358,7 @@ module Jobs
           begin
             until queue.empty?
               queued_klass, queued_opts = queue.pop(true)
-              queued_klass.new.perform(queued_opts)
+              queued_klass.new.perform_immediately(queued_opts)
             end
           ensure
             Thread.current[:discourse_nested_job_queue] = nil

spec/jobs/create_linked_topic_spec.rb

@@ -2,7 +2,7 @@
 
 RSpec.describe Jobs::CreateLinkedTopic do
   it "returns when the post cannot be found" do
-    expect { Jobs::CreateLinkedTopic.new.perform(post_id: 1, sync_exec: true) }.not_to raise_error
+    expect { Jobs::CreateLinkedTopic.new.execute(post_id: 1) }.not_to raise_error
   end
 
   context "with a post" do

spec/jobs/jobs_base_spec.rb

@@ -59,12 +59,12 @@ RSpec.describe ::Jobs::Base do
 
   it "delegates the process call to execute" do
     ::Jobs::Base.any_instance.expects(:execute).with({ "hello" => "world" })
-    ::Jobs::Base.new.perform("hello" => "world", "sync_exec" => true)
+    ::Jobs::Base.new.perform("hello" => "world")
   end
 
   it "converts to an indifferent access hash" do
     ::Jobs::Base.any_instance.expects(:execute).with(instance_of(HashWithIndifferentAccess))
-    ::Jobs::Base.new.perform("hello" => "world", "sync_exec" => true)
+    ::Jobs::Base.new.perform("hello" => "world")
   end
 
   context "with fake jobs" do

spec/jobs/jobs_spec.rb

@@ -101,8 +101,9 @@ RSpec.describe Jobs do
       it "executes the job right away" do
         Jobs::ProcessPost
           .any_instance
-          .expects(:perform)
-          .with({ "post_id" => 1, "sync_exec" => true, "current_site_id" => "default" })
+          .expects(:perform_immediately)
+          .with({ "post_id" => 1, "current_site_id" => "default" })
+
         Jobs.enqueue(:process_post, post_id: 1)
       end
 

spec/jobs/process_post_spec.rb

@@ -2,7 +2,7 @@
 
 RSpec.describe Jobs::ProcessPost do
   it "returns when the post cannot be found" do
-    expect { Jobs::ProcessPost.new.perform(post_id: 1, sync_exec: true) }.not_to raise_error
+    expect { Jobs::ProcessPost.new.execute(post_id: 1) }.not_to raise_error
   end
 
   context "with a post" do