fix(tray): Fix macOS material choice for tray menu background

[claucambra]

Summary

After (liquid glass, macOS 26+)

Before (no liquid glass)

After (visual effect material fix)

Before

Checklist

• Sign-off message is added to all commits.
• The commit history is clean with no merge commits.
  • How to rebase your commits
  • How to squash commits with rebase
• Uploaded screenshots from before and after for UI changes.
• Documentation has been updated or is not required.
• Backports requested where applicable (critical bugfixes).
• Labels added where applicable (bug/enhancement).
• Milestone added for target version.

AI (if applicable)

• The content of this PR was partly or fully generated using AI
  • I have read the guidelines for AI-assisted contributions.
  • I have read Nextcloud's AI Contribution Policy.

[github-actions]

Artifact containing the AppImage: nextcloud-appimage-pr-10359.zip

Digest: sha256:ec77f8a7f46e706b7987447e8818e28b5600b4ef886d632cc2baec7280332ee2

To test this change/fix you can download the above artifact file, unzip it, and run it.

Please make sure to quit your existing Nextcloud app and backup your data.

[Rello]

looks much nicer. tx

[Rello]

/backport to stable-34.0

[github-actions]

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