fix: use safe module access in ensureRootLogger for parallel test execution

In parallel test execution with stitched builds, sys.modules[__name__] can
raise KeyError if the module isn't yet registered in sys.modules due to
race conditions. Use sys.modules.get(__name__) instead with a None check,
following the same pattern used elsewhere in the codebase (line 734).

This fixes intermittent test failures in ensureRootLogger when tests run
in parallel with pytest -n auto in stitched mode.

Author: InertSloth

src/apathetic_logging/logger.py

@@ -950,8 +950,9 @@ class MyLogger(apathetic_logging.Logger):
 
         # Mark that user has explicitly configured the root logger
         # This tells extendLoggingModule() not to touch the root logger
-        current_module = sys.modules[__name__]
-        current_module._root_logger_user_configured = True  # type: ignore[attr-defined]  # noqa: SLF001
+        current_module = sys.modules.get(__name__)
+        if current_module is not None:
+            current_module._root_logger_user_configured = True  # type: ignore[attr-defined]  # noqa: SLF001
 
     def determineLogLevel(
         self,