[stable30] fix(css): make scrollbar visible again

[Ornanovitch]

• Manual backport of fix(css): make scrollbar visible again #47617

This is my first manual backport, I couldn't make it with the official recommendations because I had an infinite list of conflicts (perhaps because I was previously working from a fork?)

Summary

Let the browser do its job regarding the appearance of the scrollbar

TODO

• compile css

Error when I try npm run sass:

> nextcloud@1.0.0 sass
> sass --style compressed --load-path core/css core/css/ $(for cssdir in $(find apps -mindepth 2 -maxdepth 2 -name "css"); do if ! $(git check-ignore -q $cssdir); then printf "$cssdir "; fi; done)

Error: Can't find stylesheet to import.
   ╷
15 │ @import '../../node_modules/@nextcloud/dialogs/dist/style';
   │         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   ╵
  core/css/server.scss 15:9  root stylesheet

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[susnux]

/compile

[AndyScherzinger]

/compile

[github-actions]

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