Configure DrupalCI to test patches in the issue queue

Currently, D8 patches posted in the issue queue are NOT TESTED. So we're missing out on one of the biggest benefits of DrupalCI, which is automated testing of patches BEFORE they are committed or reviewed - allowing the person who submitted the patch to fix it before the community spends a lot of effort on reviewing.

This is very important for projects like this which have limited maintainer resources.

I suggest editing this test: 8.x-3.x PHP 7.2 & MySQL 5.7, D8.9 tested on commit
and changing it to this: 8.x-3.x PHP 7.2 & MySQL 5.7, D8.9 tested on commit, issue testing default