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 so dependency updates are consolidated into fewer PRs, mirroring the setup from yiisoft/package-template.

Changes:

• Group all GitHub Actions updates into a single Dependabot PR.
• Group all Composer dependency updates into a single Dependabot PR.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (98f6533) to head (ee7ab9c).

Additional details and impacted files

@@             Coverage Diff             @@
##              master      #122   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity       100       100           
===========================================
  Files              6         6           
  Lines            290       290           
===========================================
  Hits             290       290           

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