Some tests fail with non-default system/global git configuration

[timlag1305]

Hi, I was trying to run the alire tests after building by following.

I changed my global git configuration to use the main branch as the default branch instead of master. Note, that master is still the default branch on a standard git installation. To make these tests more reproducible, GIT_CONFIG_GLOBAL and GIT_CONFIG_SYSTEM can be set to /dev/null to ignore any of those settings such as changing the default branch. See git/git@4179b48 for more information.

I was able to fix two failed tests (publish__local-repo-nonstd, publish__local-repo) by running GIT_CONFIG_GLOBAL=/dev/null GIT_CONFIG_SYSTEM=/dev/null ./run.py, but it would be nice if that was handled by the run.py script.