ci: Don't try running check-code-style in a copied git repo
Because the git commands to set up check-code-style will fail:
fatal: detected dubious ownership in repository ...
and not even get to running check-style.py.
Closes: #2839 (closed), #2844 (closed)
Fixes: 86b77f65
Inspired by: !3126 (merged)
Edited by Daniel van Vugt