Treat warnings as errors in CI.

Author: sharpjs

.github/workflows/build.yaml

@@ -74,6 +74,7 @@ jobs:
       - name: Build
         run: >
           dotnet build --no-restore -c Release
+          -p:TreatWarningsAsErrors=true
           -p:PackageOutputPath=${{ runner.temp }}\dist
 
       - name: Test