Re-export dateutil._common.weekday from dateutil.relativedelta (#9819)

stubs/python-dateutil/@tests/test_cases/check_relativedelta.py

@@ -0,0 +1,9 @@
+from __future__ import annotations
+
+from dateutil import relativedelta
+
+
+# An illustrative example for why we re-export dateutil._common.weekday from dateutil.relativedelta in the stub
+class Calendar:
+    def __init__(self, week_start: relativedelta.weekday = relativedelta.MO) -> None:
+        self.week_start = week_start