Drop support for Drupal 9

Drupal 10.0 will actually also be EOL by December 11, but probably better to keep that a follow-up – see 📌 Increase Drupal core version requirement to 10.1 Fixed .
Seems we don’t have any Drupal 10.0 dependencies in our open issues, so apart from the core_version_requirement changes this patch just uses new PHP 8.0/8.1 features in several places (plus fixing a few unrelated code style issues I found on the way). I expect there are several other places that I missed, but would have had to go through the whole module otherwise.

The last submitted patch, 2: 3394189-2--raise_core_requirement_to_10_0.patch, failed testing. View results →

Merged.

Automatically closed - issue fixed for 2 weeks with no activity.