Possibility to fail `test` if anything goes wrong.

`planemo test` is currently successful if there are errors like:

- `Exception: The tool XYZ targets version 21.09 of Galaxy, you should upgrade Galaxy to ensure proper functioning of this tool.`
- or in case of xml parsing errors (which would be covered by the linter)
- ...?

Currently Galaxy only prints a warning to the logs, it would be nice if we could configure the Galaxy that is spun up for the tests such that it fails (crashes?) in such cases.

Guess this would require changes to planemo and Galaxy.

Still, there is then the problem how to use this in CI, since the test job ignores the exit code of planemo test (at the moment) .. maybe record it and use in the `combine_outputs` job.