Pin setup-msbuild to Visual Studio 18+

Add a `with: vs-version: '[18.0,)'` to the microsoft/setup-msbuild step in the CI workflow. This ensures the action uses Visual Studio 18 (VS2026) or newer when adding MSBuild to PATH, aligning the runner environment with project requirements.

Author: emako

.github/workflows/msbuild.yml

@@ -34,6 +34,8 @@ jobs:
 
     - name: Add MSBuild to PATH
       uses: microsoft/setup-msbuild@v3
+      with:
+        vs-version: '[18.0,)' # VS2026+
 
     - name: Restore NuGet packages
       working-directory: ${{env.GITHUB_WORKSPACE}}