[petsc-dev] note on submiting gitlab pipelines

[Balay, Satish]

A note to all petsc developers @gitlab who start test pipelines on
MRs:

Please rebase the MR branch over latest master (or maint - if
appropriate) before starting the test pipeline pipeline to use latest
ci fixes.

i.e make sure e73aa2c6ed is in your branch - when the test is done.
Without this fix - you might see a success status even-though some
have tests failed. [so the results would be useless].

One way to check if your branch has this fix:

git branch --contains e73aa2c6ed <branch-name>

thanks,
Satish