Retry busy app-server test executable spawns (#37354)

## Why

App-server integration tests can encounter a transient `ExecutableFileBusy`
error while starting their server process.

## What changed

Retry that specific spawn failure up to twice with a 10 ms delay, while
returning all other spawn errors immediately.

GitOrigin-RevId: 0982a9fe66bae4c41f556c845d12fb515dbf752c

codex-rs/app-server/tests/common/test_app_server.rs

@@ -257,10 +257,20 @@ impl TestAppServer {
             }
         }
 
-        let mut process = cmd
-            .kill_on_drop(true)
-            .spawn()
-            .context("codex-mcp-server proc should start")?;
+        cmd.kill_on_drop(true);
+        let mut retries = 0;
+        let mut process = loop {
+            let process = cmd.spawn();
+            if !process
+                .as_ref()
+                .is_err_and(|error| error.kind() == std::io::ErrorKind::ExecutableFileBusy)
+                || retries == 2
+            {
+                break process.context("codex-mcp-server proc should start")?;
+            }
+            retries += 1;
+            tokio::time::sleep(Duration::from_millis(10)).await;
+        };
         let stdin = process
             .stdin
             .take()