tests/functional2/lang: fix wrong unused file error for generic test group collection

Change-Id: I1c548fcebe45d2a6621987091e3a852b8a9b5765

tests/functional2/lang/lang_util.py

@@ -361,6 +361,7 @@ def _collect_generic_test_group(folder: Path) -> tuple[list[LangTest], list[Inva
                 # Skipping collection to avoid duplicate collection
                 # when both `.err.exp` and `.out.exp` are provided
                 # in case of non-error traces
+                unused -= {file.name}
                 continue
             collected |= {test_name}
             full_name = LANG_TEST_ID_PATTERN.format(folder_name=parent_name, test_name=test_name)

tests/functional2/lang/test_lang_infra.py

@@ -858,4 +858,5 @@ def test_generic_missing_in_file(pytest_command: Command):
     )
 )
 def test_generic_no_duplicate_collection(pytest_command: Command):
-    pytest_command.run().ok()
+    res = pytest_command.run().ok()
+    assert "test_invalid_configuration[name0-reasons0] SKIPPED" in res.stdout_plain