Add regex support to --xfails-file

[crusaderky]

As discussed in data-apis/array-api-compat#253
@ev-br

[ev-br]

Before trying to understand how it works, I'd like to understand how it is meant to help data-apis/array-api-compat#253. Mind elaborating please @crusaderky ?

[crusaderky]

The original intent was to add to the xfails file

.*not implemented for 'UInt16' 

However I now realise that

• this PR wouldn't achieve that: the match is on test name+parametrize; not on error raised
• the dtype iteration is performed by hypothesis and not by parametrize which means ignoring such an error would neuter the test for all other dtypes.