Support username and password from keyring

[stollero]

Hello everyone,

this brings back the enhancement added with #713 that broke with f59508b9a76bdb1a706482d254964d8a3515342c.

Had minor problems getting the tests to run because https://hatch.pypa.io/latest/community/contributing/ is outdated, but https://github.com/pypa/hatch/blob/master/docs/community/contributing.md worked 👍.

[ofek]

Yes please

[funkyfuture]

@ofek not sure whether i wasn't loud enough. this is a fine fix for a regression i introduced and i would be thankful if it could get merged.