Turn RequiredStatusChecks Checks and Contexts into pointers

[emmahsax]

By making the both Contexts and Checks pointers, the JSON will allow sending an empty slice as [] to the GitHub API, instead of taking those out and sending nil or null.

This will actually solve both #2976 and #2467.

I also clarified in the comments that empty slices are allowed, implying that if the user wants to set no checks or contexts, to allow passing an empty slice.

These changes allow the Go API to properly reflect the behavior of the GitHub API.

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[gmlewis]

Thank you, @emmahsax !
Please run the commands in step 4 found in CONTRIBUTING.md and then we should be ready for a second LGTM+Approval before merging.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2b8c7fa) 97.72% compared to head (4741b40) 98.00%.
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3070      +/-   ##
==========================================
+ Coverage   97.72%   98.00%   +0.27%     
==========================================
  Files         153      153              
  Lines       13390    10803    -2587     
==========================================
- Hits        13085    10587    -2498     
+ Misses        215      126      -89     
  Partials       90       90              

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[gmlewis]

Thank you, @emmahsax !
LGTM.

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

[valbeat]

LGTM!

[gmlewis]

Thank you, @valbeat !
Merging.

[ttomsu]

Hi @gmlewis ! Could we get this released in a v60 release soon? Thank you!

[gmlewis]

Hi @gmlewis ! Could we get this released in a v60 release soon? Thank you!

@ttomsu - this is now available in: https://github.com/google/go-github/releases/tag/v60.0.0