Add composer caching for GitHub Actions that use `runTests.sh` now

[kanow]

Goal

We want to have composer cache again for running github actions. We switched to execute actions with runTests.sh.

Acceptance Criteria

• [ ] Composer packages are cached betweeen all builds that do a composer install/update.
• [ ] We continue to use our cache key schema (TYPO3 version, PHP version, highest/lowest).
• [ ] The code coverage collection build also uses this cache.

Additional Information

This is what runTests.sh uses: -e COMPOSER_CACHE_DIR=.cache/composer