ci: fixes and cleanup

[justlevine]

What

This PR

1. Fixes the phpunit job to fail if npm run test:php fails
2. Cleans up some unnecessary caching values that leaked in from wordpress-develop.
3. Updates the job comments to reflect the current state of the jobs.

Why

• dev: use WP_Abilities_Registry::$instance instead of adding a new global #19 (comment)
• Part of Scaffold repository tooling #13

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (trunk@77640b9). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff            @@
##             trunk      #26   +/-   ##
========================================
  Coverage         ?   90.66%           
  Complexity       ?       99           
========================================
  Files            ?        7           
  Lines            ?      557           
  Branches         ?        0           
========================================
  Hits             ?      505           
  Misses           ?       52           
  Partials         ?        0           

Flag	Coverage Δ
unit	90.66% <ø> (?)

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[justlevine]

Test proof: https://github.com/justlevine/abilities-api/pull/5/checks?sha=9604687f7537621480263bcf86709a935d707ed3 shows #19 failing as it should have at that state.

[gziolo]

Nice!