Update .gitlab-ci.yml

The real reason for doing this is because there's a deprecated function in use by the module. phpstan flags it as a failure. Since failures aren't allowed all MRs will appear to fail right now. But the Core change was made only in D11, so we can't change it without breaking D10 support. The warning needs to be suppressed.

While we're at it, the tests that are enabled in .gitlab-ci.yml should be expanded to ensure modules get tested against all the supported versions of Drupal Core.