feat: Add do_not_enforce_on_create to required status checks rule params

[MattMencel]

Fixes: #3244.

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

[gmlewis]

I signed the CLA. The fmttest 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 fmttest 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.