I have a bunch of issues with the mustache linting too. I don't know enough about Mustache/Ionic to know how to fix it while still passing the basic HTML validator. Sadly, I do know how to get it to ignore specific files when the action runs via MUSTACHE_IGNORE_NAME. Example: https://github.com/ncstate-delta/moodle-mod_zoom/blob/f17423064ab34c648abbf527b82a54b5a0d71433/.github/workflows/ci.yml#L80
For the "file is stale and needs to be rebuilt", that means that your compiled versions don't match Moodle's dynamically compiled versions. Moodle very recently applied changes to almost all of the branches for the JavaScript binary formats because there was an issue with a library that's no longer supported. The fun part is that if you are running any tests against Moodle's master or MOODLE_400_STABLE branches, it is likely to give you different results because they dropped support for older browsers. Our plans is to continue shipping the version of the JavaScript in our plugin that maintains backwards compatibility for those older browsers until Moodle releases a Moodle LTS version with those changes (which should be Moodle 4.1).
For the "file is stale and needs to be rebuilt", that means that your compiled versions don't match Moodle's dynamically compiled versions. Moodle very recently applied changes to almost all of the branches for the JavaScript binary formats because there was an issue with a library that's no longer supported. The fun part is that if you are running any tests against Moodle's master or MOODLE_400_STABLE branches, it is likely to give you different results because they dropped support for older browsers. Our plans is to continue shipping the version of the JavaScript in our plugin that maintains backwards compatibility for those older browsers until Moodle releases a Moodle LTS version with those changes (which should be Moodle 4.1).