Omit OpenID Connect customization template claims when none are set

[F21]

There's a bug in the OpenID Connect customization template in #2615 where included_claim_keys is set to nil and sent to the GitHub API if it is not set. This results in the API returning a 422 Unprocessable Entity error.

This PR resolves this by setting the JSON annotation of IncludeClaimKeys in OIDCSubjectClaimCustomTemplate to omitempty and adds a test to verify this.

[codecov]

Codecov Report

Merging #2620 (d239547) into master (8ec1e49) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head d239547 differs from pull request most recent head 34c3e7f. Consider uploading reports for the commit 34c3e7f to get more accurate results

@@           Coverage Diff           @@
##           master    #2620   +/-   ##
=======================================
  Coverage   98.01%   98.02%           
=======================================
  Files         128      129    +1     
  Lines       11055    11084   +29     
=======================================
+ Hits        10836    10865   +29     
  Misses        150      150           
  Partials       69       69           

Impacted Files	Coverage Δ
github/actions_oidc.go	100.00% <100.00%> (ø)

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[gmlewis]

Thank you, @F21 !
One minor tweak, please, then we will be ready for a second LGTM+Approval from any other contributor to this repo before merging.

[F21]

Thanks for the quick review @gmlewis ! Pushed another commit to remove the blank line.

[gmlewis]

Thank you, @F21 ! (for future PRs, there's no need to force-push in this repo since we always squash-and-merge at the end anyway, just FYI... no biggie.)
LGTM.

Awaiting second LGTM+Approval from any other contributor to this repo before merging.

[valbeat]

LGTM!

[gmlewis]

Thank you, @valbeat !
Merging.