Do not panic when sending X11 WM hints fails

[warp-agent-staging]

Prevents X11 request_user_attention from panicking when WmHints::set cannot send because the X connection has died. Successful sends continue to discard the asynchronous cookie without checking it.

Warp consumes this revision in warpdotdev/warp-for-benchmarks#52.

• Tested on all platforms changed — cargo test --no-default-features --features=x11
• Added an entry to the changelog module if knowledge of this change could be valuable to users — internal error-handling fix only
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior — no API or documented behavior changes
• Created or updated an example program if it would help users understand this functionality — not applicable to a dead-connection error path
• Updated feature matrix, if new features were added or implemented — no feature change

Validation

• cargo test --no-default-features --features=x11
• cargo clippy --all-targets --no-default-features --features=x11 -- -Dwarnings
• cargo fmt

A focused automated regression test would require a real X server connection that is terminated during the request or a production-only connection seam, so this change relies on the X11 compile/test coverage above.

[warp-agent-staging]

This PR was generated with Warp.

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