CI builds are failing due to dubious ownership in repository at '/app'

[kouralex]

It seems like there has been a change in how Git works in CI builds since https://github.com/NatLibFi/Skosmos/actions/runs/3544077105/jobs/5951055820 as builds will now fail with following errors:

1) ModelTest::testGetVersion
PHPUnit\Framework\Exception: fatal: detected dubious ownership in repository at '/app'
To add an exception for this directory, call:

	git config --global --add safe.directory /app

2) WebControllerTest::testExecuteGitModifiedDateCommand
PHPUnit\Framework\Exception: fatal: detected dubious ownership in repository at '/app'
To add an exception for this directory, call:

	git config --global --add safe.directory /app

As a consequence, all CI builds will now fail.