Fix MCP cancellation tests to use the metadata callback (#56292)

Update both `call_tool` invocations in `dropping_tool_call_cancels_remote_request` to pass `|_| Ok(None)`, matching the metadata callback API while continuing to omit metadata.

GitOrigin-RevId: 9d0f3e3108fe81972ce4fd4cca13f4b7febcc616

codex-rs/rmcp-client/src/user_verification_cancellation_tests.rs

@@ -99,7 +99,7 @@ async fn dropping_tool_call_cancels_remote_request() -> anyhow::Result<()> {
         let mut call = Box::pin(client.call_tool(
             "wait".into(),
             /*arguments*/ None,
-            /*meta*/ None,
+            |_| Ok(None),
             /*timeout*/ None,
         ));
         // Drop before yielding to the transport's independently scheduled send tasks.
@@ -125,7 +125,7 @@ async fn dropping_tool_call_cancels_remote_request() -> anyhow::Result<()> {
         let mut next = Box::pin(client.call_tool(
             "next".into(),
             /*arguments*/ None,
-            /*meta*/ None,
+            |_| Ok(None),
             /*timeout*/ None,
         ));
         let request = tokio::select! {