fix: sync engine readonly folder file deletion

[guruz]

Resolves

This is for #7797 and #10099

It would probably be good to backport this (if it's the correct fix and is merged...)

Summary

Show stray file in UI instead of agressively deleting it (= potential data loss)

Checklist

• Sign-off message is added to all commits.
• The commit history is clean with no merge commits.
  • How to rebase your commits
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• 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).
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[guruz]

I'll look at the test failure..

[guruz]

I've made the code distinct between totally new file and move of existing file from same sync folder to the readonly dir.
In the latter case, the file will be deleted and restored at original location.
(EDIT: Also added explicit test for this restore case into PermissionsTest)

I've also enabled the PermissionsTest on MacOS since they now all pass on my machine. Let's see if the CI sees it differently?

(I also rebased on master)

[github-actions]

Artifact containing the AppImage: nextcloud-appimage-pr-10226.zip

Digest: sha256:d09f4f55cf3c4bf7aade303b1b0cc26ccd4b5099f2e1e011ce8ace6796b0e4e5

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

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