mypy: fix new warnings due to external type updates

nominatim/db/async_connection.py

@@ -94,7 +94,8 @@ class DBConnection:
 
         # Use a dict to hand in the parameters because async is a reserved
         # word in Python3.
-        self.conn = psycopg2.connect(**{'dsn': self.dsn, 'async': True})
+        self.conn = psycopg2.connect(**{'dsn': self.dsn, 'async': True}) # type: ignore
+        assert self.conn
         self.wait()
 
         if cursor_factory is not None:

nominatim/db/connection.py

@@ -189,7 +189,7 @@ def connect(dsn: str) -> ConnectionContext:
     try:
         conn = psycopg2.connect(dsn, connection_factory=Connection)
         ctxmgr = cast(ConnectionContext, contextlib.closing(conn))
-        ctxmgr.connection = cast(Connection, conn)
+        ctxmgr.connection = conn
         return ctxmgr
     except psycopg2.OperationalError as err:
         raise UsageError(f"Cannot connect to database: {err}") from err