Remove string literal

Author: holtskinner

src/a2a/server/apps/jsonrpc/jsonrpc_app.py

@@ -428,7 +428,7 @@ def build(
         agent_card_url: str = '/.well-known/agent.json',
         rpc_url: str = '/',
         **kwargs: Any,
-    ) -> 'FastAPI' | Starlette':
+    ) -> FastAPI | Starlette:
         """Builds and returns the JSONRPC application instance.
 
         Args: