adding an msys2 build

[K20shores]

There is a failing action on musica on mysy2 specifically in debug. I thought I could replicate it here. I can't, but it's still a good test to add

[github-actions]

📄 Documentation for this branch is available at: https://ncar.github.io/MechanismConfiguration/branch/msys2_tests/

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.95%. Comparing base (74a8604) to head (c63b166).
⚠️ Report is 70 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #136   +/-   ##
=======================================
  Coverage   86.95%   86.95%           
=======================================
  Files           3        3           
  Lines          23       23           
=======================================
  Hits           20       20           
  Misses          3        3           

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull Request Overview

This pull request adds MSYS2 build support to the existing Windows CI workflow to help debug failures observed in the musica project. The changes expand the Windows testing matrix to include both MSVC and MSYS2 toolchains.

• Renames the existing Windows job from "build-and-test" to "msvc" for clarity
• Adds Debug build configuration to the MSVC build matrix
• Introduces a new "msys2" job that builds and tests using the MinGW toolchain

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}