Enhance the 'unparsable line' error message

Author: HugoGGuerrier

lkql_checker/src/gnatcheck-compiler.adb

@@ -280,7 +280,7 @@ package body Gnatcheck.Compiler is
 
          procedure Format_Error is
          begin
-            Error ("Unparsable line: " & Msg);
+            Error ("unparsable worker output: """ & Msg & """");
             Errors := True;
          end Format_Error;
 

testsuite/tests/gnatcheck_errors/unparsable_worker_messages/test.out

@@ -1,3 +1,3 @@
-gnatcheck: Unparsable line: This line is not parsable
-gnatcheck: Unparsable line: Message: should appear
-gnatcheck: Unparsable line: This line is not parsable either
+gnatcheck: unparsable worker output: "This line is not parsable"
+gnatcheck: unparsable worker output: "Message: should appear"
+gnatcheck: unparsable worker output: "This line is not parsable either"