Reduce dependabot frequency

[martincostello]

Reduce dependabot from daily to monthly.

[Copilot]

Pull Request Overview

This PR updates the Dependabot configuration to reduce the frequency of dependency updates from daily to monthly.

• Removed the daily interval (and its associated time setting) for GitHub Actions and xunit pattern updates.
• Set the update interval to monthly while retaining the timezone for scheduled updates.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.32%. Comparing base (111b026) to head (6af37c3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1031   +/-   ##
=======================================
  Coverage   99.32%   99.32%           
=======================================
  Files          15       15           
  Lines         886      886           
  Branches      204      204           
=======================================
  Hits          880      880           
  Misses          4        4           
  Partials        2        2           

Flag	Coverage Δ
linux	99.32% <ø> (ø)
macos	99.32% <ø> (ø)
windows	99.32% <ø> (ø)

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