[stable34] fix(theming): read cachebuster as int in manifest endpoint

[backportbot]

Backport of PR #61007

[susnux]

/backport to stable33

[backportbot]

The backport to stable33 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable33
git pull origin stable33

# Create the new backport branch
git checkout -b backport/61010/stable33

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 8fdb9e1c

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/61010/stable33

Error: Failed to check for changes with origin/stable33: No changes found in backport branch

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.