fix: use dot net 6.0.x for github actions

.github/workflows/dotnet-core.yml

@@ -18,7 +18,7 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 5.0.x
+        dotnet-version: 6.0.x
     - name: Install dependencies
       run: dotnet restore Bot/Valkyrja.discord.csproj
     - name: Build