WIP: Depend on buildstream2 instead of buildstream
This is a sister merge request to buildstream!1279 (closed)
This tests that the cross-integration of tests still works but it is currently done by using the unmerged tristan/bst2-separation
branch of BuildStream...
both branches contain a "DO NOT MERGE" commit, this one contains a DO NOT MERGE commit which tests bst-plugins-template
against the bst2-separation
branch of BuildStream, and buildstream!1279 (closed) contains a similar DO NOT MERGE commit.
When it is time to merge buildstream!1279 (closed), we will have to just remove the DO NOT MERGE commits from both branches and merge them at the same time, after ensuring that CI passes at the time (at least that is an easy way to do it).