CI: drop jruby-9.4 testing

jruby-9.4 is always updated to the latest patch release of JRuby. In the
past, patch releases often include breaking changes for us. To not block
CI, We explicitly list the the patche releases we want to test against
and not jruby-9.4 anymore.

Author: bastelfreak

.github/workflows/tests.yaml

@@ -45,7 +45,6 @@ jobs:
           - {os: ubuntu-24.04, ruby: '3.2'}
           - {os: ubuntu-24.04, ruby: '3.3'}
           - {os: ubuntu-24.04, ruby: '3.4'}
-          - {os: ubuntu-24.04, ruby: 'jruby-9.4'}
           - {os: ubuntu-24.04, ruby: 'jruby-9.4.8.0'}
           - {os: ubuntu-24.04, ruby: 'jruby-9.4.13.0'}
           - {os: ubuntu-24.04, ruby: 'jruby-9.4.14.0'}