Allow commits with invalid timezones to be pushed

In the past, some git clients used to output bad timezones in the author and committer fields under special circumstances. While the error has been fixed several years ago already, there are repositories which have such broken commits in their histories. As git-receive-pack complains about such objects when running with "receive.fsckObjects=true", which is our default, users cannot push such repos to GitLab.

Disabling the object checks entirely is a bad idea, especially so as they also verify that no objects are being pushed that try to exploit known security vulnerabilities. Instead, this commit selectively disables the check for bad timezones by setting "receive.fsck.badTimezone=ignore".

Fixes gitlab#31583 (closed)