test: modernize phpunit-autotest.xml

[joshtrichards]

• Resolves: #

Summary

• Changed <directory>../apps/</directory> --> <directory>../apps/*/tests</directory> for explicit test collection: faster and clearer.
• Updated schema version to to match running version
• Added some comments for clarity/maintainability.

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)