Git should be configured to trust the /var/www/html directory

[NeillM]

When initialising behat and tunit tests the following message is displayed

The repository at "/var/www/html" does not have the correct ownership and git refuses to use it:
fatal: detected dubious ownership in repository at '/var/www/html'
To add an exception for this directory, call:
git config --global --add safe.directory /var/www/html

It seems we probably want to make git on the image trust the directory so that git can be used by composer as a fallback when initialising the test suites.