blessed builds: Does not stash build artifacts

Sigh, I had another look at the blessed build scripts. In contrast to the CI build script these fail to stash build artifacts but execute the upload script in a separte step. So while this can work (and usually does) it's just luck. This is how it should be done:

https://source.puri.sm/Librem5/deb-build-jobs/-/blob/master/ci_build.groovy#L151

So while !222 (merged) is nice for not wasting resouces (and hence speeding up builds) we need to stash things for this to work reliably.

/cc @martin.kepplinger since this is what happens with the kernel builds:

Running on Jenkins in /var/lib/jenkins/workspace/Builds/debs/deb-linux-kernel-amber-phone-staging-aarch64@2
... [ kernel build ] ...
Running on Jenkins in /var/lib/jenkins/workspace/Builds/debs/deb-linux-kernel-amber-phone-staging-aarch64@3
[Pipeline] {
[Pipeline] archiveArtifacts
Archiving artifacts
‘*.deb’ doesn’t match anything