refactor: update default user agent header to match convention (#164)

Co-authored-by: larkee <larkee@users.noreply.github.com>

Author: larkee

google/cloud/sqlalchemy_spanner/sqlalchemy_spanner.py

@@ -549,7 +549,7 @@ def create_connect_args(self, url):
         dist = pkg_resources.get_distribution("sqlalchemy-spanner")
         return (
             [match.group("instance"), match.group("database"), match.group("project")],
-            {"user_agent": dist.project_name + "/" + dist.version},
+            {"user_agent": f"gl-{dist.project_name}/{dist.version}"},
         )
 
     @engine_to_connection

test/test_suite.py

@@ -1575,7 +1575,7 @@ def test_user_agent(self):
         with self._engine.connect() as connection:
             assert (
                 connection.connection.instance._client._client_info.user_agent
-                == dist.project_name + "/" + dist.version
+                == f"gl-{dist.project_name}/{dist.version}"
             )