[Mesa-ci-intel] Add staging/19.1 branch to the CI

[Juan A. Suarez Romero]

Hello.


I've made a new branch, staging/19.1, that contains a candidate branch point for
the next 19.1 series.

Could it be possible to set up the CI to test this branch?

If everything goes fine, this could be the first RC for 19.1.0 release.

Thanks in advance!


	J.A.