Add missing expires_at field to github.Authorization

[t0rr3sp3dr0]

The response of client.Authorizations.Check(...) should contain the expires_at field.

https://docs.github.com/en/rest/apps/oauth-applications?apiVersion=2022-11-28#check-a-token

[gmlewis]

Please run step 4 of CONTRIBUTING.md and push the results to this PR.
Thank you, @t0rr3sp3dr0 !

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.95%. Comparing base (2b8c7fa) to head (9b95df2).
Report is 129 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3251      +/-   ##
==========================================
- Coverage   97.72%   92.95%   -4.78%     
==========================================
  Files         153      171      +18     
  Lines       13390    11647    -1743     
==========================================
- Hits        13085    10826    -2259     
- Misses        215      727     +512     
- Partials       90       94       +4     

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[gmlewis]

This PR will be closed and marked as abandoned if no response by next week.