Fix deprecations for watchdog_exception and HttpKernelInterface::MASTER_REQUEST

These changes would mean we have to drop the Drupal 9 support. I think this seems fine but maybe we want a new major version to do that.

Re-titling issue to make it clear what is happening. I think dropping D9 support is okay because it is now unsupported.

So 🌱 Guidelines for semantic versioning and Drupal core support Active led to https://www.drupal.org/docs/develop/managing-a-drupalorg-theme-module-or... → and technically we should do a minor release if dropping 9.x.

🤷‍♂️ although does the minor version mean anything if we merge onto 2.x and just tag 2.1.0? It's not like we're supporting 2.0.x in any true fashion and backporting fixes.

D9 is long gone that I'm +1 to doing this in a patch release.

Let's do it!

Thanks!