ci: Clone the mutter repo as user

Merged Marco Trevisan requested to merge 3v1n0/mutter:ci-fix-dist-permissions into main

Since !3016 (merged) the mutter-dist job fails because it can't access to the git repo, we can't just fix it alone because cloning as "root" before that our CI image does the job may lead to git permission errors, so handle all this manually and only when required.

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