Group Dependabot updates

[samdark]

Replicates the Dependabot grouping configuration from yiisoft/package-template so GitHub Actions updates are grouped into a single PR and Composer dependency updates are grouped into a single PR.

[Copilot]

Pull request overview

Note

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Adds Dependabot grouping rules so updates are bundled into fewer PRs, mirroring the configuration from yiisoft/package-template.

Changes:

• Group all GitHub Actions dependency updates into a single Dependabot PR.
• Group all Composer dependency updates into a single Dependabot PR.
• Fix/normalize the Composer schedule indentation while keeping the existing versioning strategy.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.29%. Comparing base (c40be5e) to head (d4a7b8b).

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #52   +/-   ##
=========================================
  Coverage     96.29%   96.29%           
  Complexity       34       34           
=========================================
  Files             3        3           
  Lines            81       81           
=========================================
  Hits             78       78           
  Misses            3        3           

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