CI: Made actions more efficient (#6124)

Updates our CI process to be more efficient by:

- Uses setupphp/node image for more direct access to desired PHP versions.
- Adds php extension caching via https://github.com/shivammathur/cache-extensions
- Reverted to using MySQL in-test-container to reduce syscalls across the container stack which seemed to be slowing things down.
- Update JS testing to only use one worker, to avoid exhausting all CPUs. I think it was attempting to use all threads on the host system before, causing the machine to lock up, since only a subset of cores were available to the environment.

Reviewed-on: https://codeberg.org/bookstack/bookstack/pulls/6124