fix: increase timeout of test_writable_root (#713)

Although we made some promising fixes in
https://github.com/openai/codex/pull/662, we are still seeing some
flakiness in `test_writable_root()`. If this continues to flake with the
more generous timeout, we should try something other than simply
increasing the timeout.

codex-rs/core/src/linux.rs

@@ -225,7 +225,9 @@ mod tests_linux {
                 &format!("echo blah > {}", file_path.to_string_lossy()),
             ],
             &[tmpdir.path().to_path_buf()],
-            500,
+            // We have seen timeouts when running this test in CI on GitHub,
+            // so we are using a generous timeout until we can diagnose further.
+            1_000,
         )
         .await;
     }