extra_data: In system-helper case, canonicalize uid/gid

Make sure all files produced by apply_extra are owned by root.

Closes: #2398
Approved by: matthiasclasen
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f