Use pytest.raises match over checking for string content manually

[matthewfeickert]

These were previously not doing anything and have to be moved outside the pytest.raises to actually work. I checked other places in the tests where the same pattern is used and there it all seemed fine.

There's also built-in functionality to do this quite conveniently:

with pytest.raises(RuntimeError, match="SigXsecOverSM"):
    ...

Originally posted by @alexander-held in #2109 (comment)

This is great and should be applied everywhere!