[reginaldalfret]

Fixes #4520

Summary

This PR adds support for the repository ruleset rule type code_quality, corresponding to the "Require code quality results" branch protection rule.

Changes

• Added RulesetRuleTypeCodeQuality RepositoryRuleType = "code_quality"
• Defined CodeQualityRuleParameters with Severity string json:"severity,omitempty"``
• Defined CodeQualityBranchRule representing the branch rule metadata and parameters
• Added CodeQuality field to RepositoryRulesetRules and BranchRules
• Handled serialization and deserialization in RepositoryRulesetRules, BranchRules, and RepositoryRule
• Added comprehensive unit tests in rules_test.go (TestCodeQualityRuleRoundTrip and TestCodeQualityRuleInvalidParameters)

[codecov]

Codecov Report

❌ Patch coverage is 68.42105% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.59%. Comparing base (28d2616) to head (2d60fd1).

Files with missing lines	Patch %	Lines
github/rules.go	68.42%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4648      +/-   ##
==========================================
- Coverage   98.62%   98.59%   -0.04%     
==========================================
  Files         201      201              
  Lines       18811    18830      +19     
==========================================
+ Hits        18553    18566      +13     
- Misses        258      264       +6     

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