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

Copilot couldn't run its full agentic review because no GitHub Actions runner was available. Make sure your repository has a runner available to run Copilot's review, or add a copilot-setup-steps.yml file specifying one with the runs-on attribute. See the docs for more details.

Adds Dependabot grouping rules so updates are bundled into fewer PRs, matching yiisoft/package-template’s setup.

Changes:

• Group all GitHub Actions dependency 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 (634657f) to head (db44d4f).

Additional details and impacted files

@@             Coverage Diff             @@
##              master       #79   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity        76        76           
===========================================
  Files              3         3           
  Lines            184       184           
===========================================
  Hits             184       184           

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