Use local config for integration test repos

Why is this change being made?

Integration tests currently alter the git user configuration globally. This makes developer's git user get changed to test@test.com when they run integration tests, which is both annoying and confusing. This MR fixes the behavior by only setting user.email and user.name locally in the newly created integration test repo.

This no longer overwrites my user config when running centos_spec.rb:

$ bundle exec rspec spec/integration/centos_spec.rb > /dev/null
warning: parser/current is loading parser/ruby27, which recognizes
warning: 2.7.3-compliant syntax, but you are running 2.7.4.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.
$ git config --list | grep user
user.name=Brian Williams
user.email=bwilliams@gitlab.com