Add CI for < 3.8

[matthewhilton]

• Various patches are required - see https://github.com/catalyst/moodle-tool_passwordvalidator#installation
• Note according to https://docs.moodle.org/dev/version.php - may not need to change, since this will alert the user that it is not 100% supported & that they need to install patches (but can continue install if they have done so)
• Then the patches can be added to the CI and the branch range extended https://github.com/catalyst/catalyst-moodle-workflows/tree/main#core-patches