Run upgrade tests on all active branches

[hasheddan]

Currently we run upgrade on the latest stable to latest master build (although the latest stable version has a tendency to get stale because it requires manual upgrade). As a "feature" of this test getting stale, we were able to catch crossplane/crossplane#2323, but if this test had been kept up to date we would not have. We should instead make sure that we are testing upgrade from every active branch to latest build.