Optimize which PHPUnit CI jobs run: 1) nightly: ALL version+DB combos, 2) 1.x/merged MRs: 11.3 all DBs, 11.2 only SQLite

Overview

Today:

• MR commit: already only SQLite, both on 11.2 + 11.3. Example: https://git.drupalcode.org/project/canvas/-/pipelines/809198
• 1.x commit: all DBs, both on 11.2 + 11.3. Example: https://git.drupalcode.org/project/canvas/-/pipelines/809167

Quoting #3585979-19: CI: review automatic jobs and when they run:

After #3529128: Speed up PHPUnit on CI; stop relying on drupal.org composer template lands, I think we should consider making:

1. PHPUnit (11.2) run on all DBs
2. PHPUnit (11.3) run only on SQLite

Or vice versa.

Thoughts?

EDIT: to clarify, I mean for merge commits (aka push to 1.x). Currently both 11.2 and 11.3 run all tests on all 4 DBs.

Proposed resolution

• unchanged MR commit: already only SQLite, both on 11.2 + 11.3
• changed 1.x commit: all DBs on 11.3 only because that's what the majority of people use, only SQLite on 11.2
• changed NEW nightly pipeline: all DBs, both on 11.2 + 11.3

User interface changes

None.