Avoid panicking on X11 attention hint send failure

[warp-agent-staging]

On Linux/X11, requesting attention after the X server disconnects panics while sending WM_HINTS. Treat the send failure as recoverable; successful sends still ignore the returned cookie as before. Warp adopts this commit in warpdotdev/warp-for-benchmarks#53.

• Tested on all platforms changed — Linux/X11 with Xvfb.
• Added an entry to the changelog module if knowledge of this change could be valuable to users — omitted for this fork-only crash fix.
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior — no API change.
• Created or updated an example program if it would help users understand this functionality — existing API usage is unchanged.
• Updated feature matrix, if new features were added or implemented — no new feature.

Validation

• The Xvfb regression test failed with Failed to set WM hints: IoError on the original code and passed after the fix.
• cargo test --no-default-features --features x11,rwh_06 --lib --test x11_user_attention (8 library tests and the regression test passed).
• cargo clippy --no-default-features --features x11,rwh_06 --lib --test x11_user_attention -- -D warnings passed.

Plans:

• Recover from X11 attention send failures and update Warp’s winit pin

[warp-agent-staging]

This PR was generated with Warp.

Comment @warp-staging-factory on this PR to send it follow-up work.