Change target frameworks to net7

Author: FreePhoenix888

.github/workflows/csharp.yml

@@ -24,7 +24,7 @@ jobs:
           submodules: true
       - name: Test
         run: |
-          dotnet test -c Release -f net6
+          dotnet test -c Release -f net7
   pushNuGetPackageToGitHubPackageRegistry:
     needs: test
     runs-on: ubuntu-latest