Was part of #4583 , but this can only be implemented, once PMD supports java 21. This is the case, once #4638 is merged (a snapshot version is sufficient, we don't need a release).

• Update https://github.com/pmd/java-regression-tests
  • Record Patterns
  • Pattern Matching for Switch
• Update build.sh to use 21 instead of 21-ea
  • For this, we need to wait for Java 21 release, which is due 2023-09-19.