build: Always include blubber.version and blubber.variant labels
Have the build.Target
always include labels for the current Blubber
version and the target variant. This restores behavior that regressed
with the native LLB refactor.
Include a basic acceptance test for this behavior.
Related MRs:
- !92 (merged)
- !91 (merged) (This MR)
- experimental/native-llb