Drop testing of 3.11

[burmanm]

What is missing?

After the release of 5.0, the 3.11 is now EOL. As we will no longer actively add any features to the 3.11 images either or support new features in it (such as running readOnlyRootFilesystem), there remains no point in testing 3.11 with newer versions of cass-operator.

As such, 1.22.x will remain the last version with 3.11 support, newer versions would not actively remove support for 3.11 or prevent deployment, but we would no longer promise support for it either.

Why is this needed?

To follow Cassandra's support lifecycle. Also, since we need to add 5.0.x to our tests, removing 3.11 will keep our test suite somewhat sanely sized.

┆Issue is synchronized with this Jira Story by Unito
┆Reviewer: Alexander Dejanovski
┆Fix Versions: 2024-10
┆Issue Number: CASS-69