feat: support new release discussions feature

[caarlos0]

support the new discussion_category_name field when creating/updating a release.

refs https://github.blog/changelog/2021-04-06-releases-support-comments-and-reactions-with-discussion-linking/
refs https://docs.github.com/en/rest/reference/repos#create-a-release
refs goreleaser/goreleaser#2161

[codecov]

Codecov Report

Merging #1856 (465a96b) into master (94d2fbb) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1856   +/-   ##
=======================================
  Coverage   97.64%   97.64%           
=======================================
  Files         105      105           
  Lines        6762     6764    +2     
=======================================
+ Hits         6603     6605    +2     
  Misses         86       86           
  Partials       73       73           

Impacted Files	Coverage Δ
github/repos_releases.go	89.37% <100.00%> (+0.13%)	⬆️

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[gmlewis]

Thank you, @caarlos0 !
LGTM.
Merging.