fix: supress only assertion and file creation error

[12rambau]

alternative to #60 that finally do what we are expecting.

1. I discover that all the files were wrongly erasing the source file with the serialized content (that's the replacement between data_name and serialized_name).
2. As recommended in use a custom error instead of calling pytest.fail ESSS/pytest-regressions#187 (comment) I catch 2 error:
   1. AssertionError which is the case where the data is not corresponding thus need to be computed from the server
   2. pytest.fail.Exception which correspond to file creation.

So in the future:

1. first run will compute the computed value
2. 2nd run will add the serialized version (as the check will not raise anything
3. 3rd +n run will only check the serialized file.

[12rambau]

@fitoprincipe I'll merge this and make a new release to at least get a working version in pypi, we can discuss in your PR the other aproach you are adertizing.