Deprecated old transaction setter

Author: antonpirker

sentry_sdk/scope.py

@@ -164,7 +164,9 @@ def transaction(self):
     def transaction(self, value):
         # type: (Any) -> None
         # would be type: (Optional[str]) -> None, see https://github.com/python/mypy/issues/3004
-        """When set this forces a specific transaction name to be set."""
+        """When set this forces a specific transaction name to be set.
+
+        Deprecated: use set_transaction_name instead."""
         # XXX: the docstring above is misleading. The implementation of
         # apply_to_event prefers an existing value of event.transaction over
         # anything set in the scope.