test(compat): mandatory error snapshot assertion

[weihanglo]

This ensures we see the expected error,
not unrelated random one.

I expect external tools won't update error messages too often,
otherwise it may cause churns

[weihanglo]

Forgot to say, this is a preparation so we can see the exact error message from git apply failure when applying control=0, rather than some other random binary diff parsing failure.
(I spent quite a while to find my control=0 patch fixture has some other issues 😓)