PYTHON-5505 Allow retry write after overload error even if sessions are not supported

Author: ShaneHarvey

pymongo/asynchronous/mongo_client.py

@@ -2915,7 +2915,7 @@ async def _write(self) -> T:
                     and conn.supports_sessions
                 )
                 is_mongos = conn.is_mongos
-                if not sessions_supported:
+                if not self._always_retryable and not sessions_supported:
                     # A retry is not possible because this server does
                     # not support sessions raise the last error.
                     self._check_last_error()

pymongo/synchronous/mongo_client.py

@@ -2905,7 +2905,7 @@ def _write(self) -> T:
                     and conn.supports_sessions
                 )
                 is_mongos = conn.is_mongos
-                if not sessions_supported:
+                if not self._always_retryable and not sessions_supported:
                     # A retry is not possible because this server does
                     # not support sessions raise the last error.
                     self._check_last_error()