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 updates are consolidated into fewer PRs, mirroring yiisoft/package-template’s behavior.

Changes:

• Group all GitHub Actions dependency updates into a single Dependabot PR.
• Add a Composer Dependabot configuration and group all Composer dependency updates into a single PR.
• Set Composer versioning strategy to increase-if-necessary with a daily schedule and cooldown.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.95%. Comparing base (544e273) to head (d613564).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #88   +/-   ##
=========================================
  Coverage     85.95%   85.95%           
  Complexity       51       51           
=========================================
  Files             1        1           
  Lines           121      121           
=========================================
  Hits            104      104           
  Misses           17       17           

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