Improve error message in case of version mismatch

[ewjoachim]

The coverage package mismatch - coverage pkg I used to generate the .coverage file was different from the one used in the action (minor version was different).

Originally posted by @dmitry-olefir-snkeos in #303 (comment)

[ewjoachim]

I'm guessing that there might be quite a few cases where it might fail, apart from version mismatch, actually. We should try and detect at least some of them.