feat: Add do_not_enforce_on_create to required status checks rule params

[MattMencel]

Fixes: #3244.

I signed the CLA. The fmt test and lint scripts all passed without warnings.

[gmlewis]

I signed the CLA. The fmt test and lint scripts all passed without warnings.

It looks like GitHub Actions disagrees:

--- FAIL: TestRepositoryRule_UnmarshalJSON (0.01s)
    --- FAIL: TestRepositoryRule_UnmarshalJSON/Valid_required_status_checks_params (0.00s)
        repos_rules_test.go:287: RepositoryRule.UnmarshalJSON expected rule &{Type:required_status_checks Parameters:0xc0004208d0 RulesetSourceType: RulesetSource: RulesetID:0}, got &{Type:required_status_checks Parameters:0xc000420d20 RulesetSourceType: RulesetSource: RulesetID:0}

Can you please update this test and push the changes to this PR?
(There's no need to force-push in this repo because we always squash-and-merge each PR.)

Thank you, @MattMencel !

[MattMencel]

I signed the CLA. The fmt test and lint scripts all passed without warnings.

It looks like GitHub Actions disagrees:

Whoopsies.... well they do now. 😄

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.95%. Comparing base (2b8c7fa) to head (5c88e6f).
Report is 101 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3245      +/-   ##
==========================================
- Coverage   97.72%   92.95%   -4.78%     
==========================================
  Files         153      171      +18     
  Lines       13390    11646    -1744     
==========================================
- Hits        13085    10825    -2260     
- Misses        215      727     +512     
- Partials       90       94       +4     

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[gmlewis]

Thank you, @MattMencel !
LGTM.
Merging.