gitlab-ci.yml: set git user/email (!1848)

Prevent upcoming tests for "pmbootstrap pull" from failing, when trying
to create a git repository.

.gitlab-ci.yml

@@ -14,6 +14,8 @@ before_script:
   - "source venv/bin/activate"
   - "pip3 install flake8 pytest-cov python-coveralls pytest"
   - "python3 --version"
+  - "su pmos -c 'git config --global user.email postmarketos-ci@localhost'"
+  - "su pmos -c 'git config --global user.name postmarketOS_CI'"
 
 stages:
   - checks