cci: Install built rpm on top of cosa

[cgwalters]

I would have sworn we were doing this before, but if so I can't find it in git logs.

We want to test the new rpm-ostree at build time too of course.

xref #5251 (comment)

[openshift-ci]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[jlebon]

This is done in the stage right before this one.

rpm-ostree/.cci.jenkinsfile

Lines 37 to 41 in e529101

	unstash 'rpms'
	// run this stage first without installing deps, so we match exactly the cosa pkgset
	// (+ our built rpm-ostree)
	shwrap("""
	dnf install -y *.rpm

[cgwalters]

Right I was misreading this as being in different pods.
So the mystery of how CI didn't catch the problem persists.