Fix automated build

Updated the dotnet framework version to 7.0.x for the GitHub build
workflow action.

Author: Gideon de Swardt

.github/workflows/dotnet-core.yml

@@ -18,7 +18,7 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: '5.0.x'
+        dotnet-version: '7.0.x'
     - name: Install dependencies
       run: dotnet restore
     - name: Build