DEV: Remove harded id when fabricating in tests (#18729)

Hardcoding ids always lead to sadness for our test suite

spec/lib/topic_view_spec.rb

@@ -1001,7 +1001,7 @@ RSpec.describe TopicView do
     subject(:topic_view) { described_class.new(topic, user) }
 
     let(:topic) { Fabricate(:topic) }
-    let(:user) { Fabricate(:user, id: 1) }
+    let(:user) { Fabricate(:user) }
     let(:category) { topic.category }
 
     before do

spec/serializers/post_serializer_spec.rb

@@ -129,7 +129,7 @@ RSpec.describe PostSerializer do
   end
 
   context "with a hidden post with add_raw enabled" do
-    let(:user) { Fabricate(:user, id: -99999) }
+    let(:user) { Fabricate(:user) }
     let(:raw)  { "Raw contents of the post." }
 
     context "with a public post" do