jobs: suppress "No suitable job" if -q is given

This allows code of the form `if jobs -q $some_pid` in scripts to check whether a previously started job is still running. Previously this would return the correct value, but also print an error message.

The invalid argument errors will still be printed.
Added test cases for both.

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Notable improvements and fixes
 - `fish --no-execute` will no longer complain about unknown commands or non-matching wildcards, as these could be defined differently at runtime (especially for functions). #977
+- `jobs --quiet PID` will no longer print 'no suitable job' if the job for PID does not exist (e.g. because it has finished). #6809
 
 ### Syntax changes and new commands
 

src/builtin_jobs.cpp

@@ -209,7 +209,9 @@ int builtin_jobs(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
                     builtin_jobs_print(j, mode, false, streams);
                     found = true;
                 } else {
-                    streams.err.append_format(_(L"%ls: No suitable job: %ls\n"), cmd, argv[i]);
+                    if (mode != JOBS_PRINT_NOTHING) {
+                        streams.err.append_format(_(L"%ls: No suitable job: %ls\n"), cmd, argv[i]);
+                    }
                     return STATUS_CMD_ERROR;
                 }
             }

tests/checks/jobs.fish

@@ -24,6 +24,21 @@ jobs -c
 #CHECK: Command
 #CHECK: sleep
 #CHECK: sleep
+jobs 1
+echo $status
+#CHECK: 1
+#CHECKERR: jobs: No suitable job: 1
+jobs foo
+echo $status
+#CHECK: 2
+#CHECKERR: jobs: 'foo' is not a valid process id
+jobs -q 1
+echo $status
+#CHECK: 1
+jobs -q foo
+echo $status
+#CHECK: 2
+#CHECKERR: jobs: 'foo' is not a valid process id
 disown foo
 #CHECKERR: disown: 'foo' is not a valid job specifier
 disown (jobs -p)