openstack: filter using metadata (#698)

Filter openstack runners by the metadata tags

runner_manager/backend/openstack.py

@@ -57,7 +57,7 @@ def list(self) -> List[Runner]:
         try:
             servers: List[Server] = list(
                 self.client.compute.servers(
-                    tags={
+                    metadata={
                         "manager": str(self.manager),
                         "runner_group": str(self.runner_group),
                     }