Add pipeline phpunit job for previous core version

MR39 ready for review. The overall pipeline now ends with amber warning not red failure. And we can see a green pass for the previous core phpunit job.

LGTM

Thanks.
After the commit, the branch test failed for both phpunit jobs with

Failed to run installer database tasks: Failed to connect to your database server. The server reports the following message: <em class="placeholder">SQLSTATE[HY000] [2002] Connection refused [Tip: This message normally means that there is no MySQL server running on the system or that you are using an incorrect host name or port number when trying to connect to the server.

I think this is unrelated to the new change.

Automatically closed - issue fixed for 2 weeks with no activity.