The installed Composer packages will be different depending on the
major TYPO3 version being tested and on the strategy for the
dependencies (highest, lowest). So it makes sense to have
separate Composer caches for these versions in order to avoid
cache misses.
Composer versions 2.2.0 and 2.2.1 have a bug that breaks PHPUnit.
Until version 2.2.2 is released with a fix, we need to keep to
Composer 2.1 to keep the tests from breaking.
See https://github.com/composer/composer/issues/10387 for details.
