Fix duplicate macro test assertions to match dbt-adapters error message

The DuplicateMacroInPackageError in dbt-adapters uses "dbt found
multiple macros named" but the tests still asserted the old wording
"dbt found two macros named". Update assertions to match.

Relates to #10387

https://claude.ai/code/session_014vwk3tJhceD1QrNWL652Qn

Author: claude

tests/functional/duplicates/test_duplicate_macro.py

@@ -41,7 +41,7 @@ def macros(self):
         }
 
     def test_duplicate_macros(self, project):
-        message = 'dbt found two macros named "some_macro" in the project'
+        message = 'dbt found multiple macros named "some_macro" in the project'
         with pytest.raises(CompilationError) as exc:
             run_dbt(["parse"])
         exc_str = " ".join(str(exc.value).split())  # flatten all whitespace
@@ -62,7 +62,7 @@ def macros(self):
         }
 
     def test_duplicate_macros(self, project):
-        message = 'dbt found two macros named "some_macro" in the project'
+        message = 'dbt found multiple macros named "some_macro" in the project'
         with pytest.raises(CompilationError) as exc:
             run_dbt(["compile"])
         exc_str = " ".join(str(exc.value).split())  # flatten all whitespace