Update pytest_httpserver/httpserver.py

Co-authored-by: Hayao <hayao_s@tokyo-gas.co.jp>

Author: csernazs

pytest_httpserver/httpserver.py

@@ -1305,7 +1305,8 @@ def dispatch(self, request: Request) -> Response:
         """
         if self._readiness_check_pending:
             self._readiness_check_pending = False
-            return Response("OK", status=200)
+            from http import HTTPStatus
+            return Response(HTTPStatus.OK.phase, status=HTTPStatus.OK.value)
 
         if self.permanently_failed:
             return self.respond_permanent_failure()