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.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5a8a6e6) to head (1664522).

Additional details and impacted files

@@              Coverage Diff               @@
##             master       #77       +/-   ##
==============================================
+ Coverage     48.54%   100.00%   +51.45%     
  Complexity       37        37               
==============================================
  Files             7         7               
  Lines           103       103               
==============================================
+ Hits             50       103       +53     
+ Misses           53         0       -53     

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[Copilot]

Pull request overview

Note

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Updates Dependabot configuration to group dependency updates similarly to yiisoft/package-template, aiming to reduce PR noise by bundling GitHub Actions and Composer updates.

Changes:

• Enable grouped GitHub Actions updates on a weekly schedule (instead of disabling via open PR limit).
• Add grouping rules for Composer updates while keeping the versioning strategy.
• Introduce cooldown settings intended to space out updates.

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