Reasons for creating this PR

GitHub Actions CI builds are currently failing because some tests are executing git commands, but git refuses to run because of a "dubious ownership" error. The error happens because the PHPUnit tests are run within a container as the root user, but the /app directory is owned by another user (uid 1001).

Here is whoami under the container:

uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel),11(floppy),20(dialout),26(tape),27(video)

Here is ls -l /app:

drwxr-xr-x   15 1001     ntp           4096 Dec 15 13:57 /app

Link to relevant issue(s), if any

• Closes CI builds are failing due to dubious ownership in repository at '/app' #1394

Description of the changes in this PR

The PR fixes the problem by first creating the directory /home/runner which doesn't exist within the container, even though it is the value of the HOME environment variable. Then it executes the command git config --global --add safe.directory /app, which will prevent git from complaining about dubious ownership; this will be stored in the configuration file /home/runner/.gitconfig where subsequent git commands (run from PHPUnit tests) will see it.

Known problems or uncertainties in this PR

n/a

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that show that the new code works, or tests are not relevant for this PR (e.g. only HTML/CSS changes)
• The PR doesn't reduce accessibility of the front-end code (e.g. tab focus, scaling to different resolutions, use of .sr-only class, color contrast)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)