Update dependabot config

[martincostello]

Re-add NuGet so that automated dependency submission works.

Can remove if/when .slnx is supported.

[Copilot]

Pull Request Overview

This PR updates the Dependabot configuration to change the package ecosystem from github-actions to nuget to enable automated dependency submission for .NET projects. This is a temporary workaround until GitHub supports .slnx files for dependency detection.

• Changes package ecosystem monitoring from GitHub Actions to NuGet packages
• Maintains yearly update schedule for dependency checks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.59%. Comparing base (bf576c5) to head (8d7e4b7).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #973   +/-   ##
=======================================
  Coverage   98.59%   98.59%           
=======================================
  Files          16       16           
  Lines         284      284           
  Branches       37       37           
=======================================
  Hits          280      280           
  Misses          2        2           
  Partials        2        2           

Flag	Coverage Δ
linux	98.59% <ø> (ø)
macos	97.88% <ø> (ø)
windows	98.59% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.