Use .NET 8 in CI

.github/workflows/ci.yml

@@ -15,6 +15,10 @@ jobs:
         include:
           - os: windows-latest
             checkTarget: true
+            # We want to use one version for most things and this latest for
+            # others. This is an ok way to test both without requiring a
+            # separate matrix permutation.
+            dotNetVersionOverride: 8.x
           - os: ubuntu-latest
             docsTarget: true
             cloudTestTarget: true
@@ -44,7 +48,7 @@ jobs:
         with:
           # Specific .NET version required because GitHub macos ARM image has
           # bad pre-installed .NET version
-          dotnet-version: 6.x
+          dotnet-version: ${{ matrix.dotNetVersionOverride || 6 }}
 
       - name: Install protoc
         uses: arduino/setup-protoc@v3