[godot] Update build dotnet SDK to 8.0.x

.github/actions/setup-godot-deps-4/action.yml

@@ -26,7 +26,7 @@ runs:
         python -m pip install scons==4.7.0
         scons --version
 
-    - name: Setup dotnet 6
+    - name: Setup dotnet 8
       uses: actions/setup-dotnet@v3
       with:
-          dotnet-version: '6.0.x'
+          dotnet-version: '8.0.x'