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 related dependency updates are bundled into fewer PRs, mirroring 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 24.35%. Comparing base (44250a4) to head (28080f9).

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #52   +/-   ##
=========================================
  Coverage     24.35%   24.35%           
  Complexity       60       60           
=========================================
  Files             6        6           
  Lines           193      193           
=========================================
  Hits             47       47           
  Misses          146      146           

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