GitHub Actions: use .NET v7.0

Author: janusw

.github/workflows/dotnet.yml

@@ -19,7 +19,7 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v3
       with:
-        dotnet-version: 6.0.x
+        dotnet-version: 7.0.x
     - name: Add msbuild to PATH
       uses: microsoft/[email protected]
     - name: Restore