ci: Fix build for the dotnet SDK and macOS runner image

[askpt]

This PR

This pull request contains several updates aimed at improving build reliability and compatibility across different environments. The most important changes include updating the .NET SDK version, adjusting the build configuration for .NET Framework 4.6.2, and updating the macOS runner for CI workflows.

Build and SDK configuration improvements:

• Updated the .NET SDK version in global.json from 9.0.300 to 9.0.306 and set rollForward to "disable" to ensure the build uses the specified SDK version exactly, improving build reproducibility.
• Added a property group in build/Common.props to suppress target framework support warnings when building for .NET Framework 4.6.2, working around build failures due to certain warnings.

CI workflow updates:

• Updated the macOS x64 runner in .github/workflows/aot-compatibility.yml from macos-13 to macos-15-intel to ensure compatibility with current GitHub-hosted runners.

Notes

We were getting errors in the latest 9.0.x.
9.0.112 -> https://github.com/open-feature/dotnet-sdk/actions/runs/19275629307
10.0.100 -> https://github.com/open-feature/dotnet-sdk/actions/runs/19275919896
9.0.111 -> https://github.com/open-feature/dotnet-sdk/actions/runs/19276071981

This attempts to lock it to the version 9.0.111 until we fully migrate to the SDK 10.0

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.25%. Comparing base (ee862f0) to head (a052a73).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #636      +/-   ##
==========================================
- Coverage   90.44%   90.25%   -0.20%     
==========================================
  Files          78       79       +1     
  Lines        3256     3284      +28     
  Branches      377      384       +7     
==========================================
+ Hits         2945     2964      +19     
- Misses        244      251       +7     
- Partials       67       69       +2     

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