Move the musl CI container to Alpine 3.24

Alpine 3.21 is the oldest Alpine the rust image still publishes and reaches
end of life in November 2026.

Signed-off-by: Claude <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014DcoycxoTMpyz66pmby8Nb

Author: claude

.github/workflows/musl.yml

@@ -29,7 +29,7 @@ jobs:
           && format('runs-on={0}/runner=amd64-large/image=ubuntu24-full-x64-pre-v2/tag=rust-build-musl', github.run_id)
           || 'ubuntu-latest' }}
     container:
-      image: ghcr.io/rust-lang/rust:1-alpine3.21
+      image: ghcr.io/rust-lang/rust:1-alpine3.24
       credentials:
         username: ${{ github.repository_owner }}
         password: ${{ secrets.GITHUB_TOKEN }}