Refer to LoggingDatabaseConnection as a string

I've imported it only if TYPE_CHECKING, to avoid a circular import.

synapse/storage/engines/_base.py

@@ -86,7 +86,7 @@ def convert_param_style(self, sql: str) -> str:
     # the Sqlite engine expects to use LoggingDatabaseConnection.cursor
     # instead of sqlite3.Connection.cursor: only the former takes a txn_name.
     @abc.abstractmethod
-    def on_new_connection(self, db_conn: LoggingDatabaseConnection) -> None:
+    def on_new_connection(self, db_conn: "LoggingDatabaseConnection") -> None:
         ...
 
     @abc.abstractmethod

synapse/storage/engines/postgres.py

@@ -142,7 +142,7 @@ def check_new_database(self, txn: Cursor) -> None:
     def convert_param_style(self, sql: str) -> str:
         return sql.replace("?", "%s")
 
-    def on_new_connection(self, db_conn: LoggingDatabaseConnection) -> None:
+    def on_new_connection(self, db_conn: "LoggingDatabaseConnection") -> None:
         db_conn.set_isolation_level(self.default_isolation_level)
 
         # Set the bytea output to escape, vs the default of hex

synapse/storage/engines/sqlite.py

@@ -85,7 +85,7 @@ def check_new_database(self, txn: Cursor) -> None:
     def convert_param_style(self, sql: str) -> str:
         return sql
 
-    def on_new_connection(self, db_conn: LoggingDatabaseConnection) -> None:
+    def on_new_connection(self, db_conn: "LoggingDatabaseConnection") -> None:
         # We need to import here to avoid an import loop.
         from synapse.storage.prepare_database import prepare_database