Fix Xcode Version

Author: TheCodeTraveler

.github/workflows/dotnet-build.yml

@@ -65,7 +65,7 @@ jobs:
         if: runner.os == 'macOS'
         uses: maxim-lobanov/setup-xcode@v1
         with:
-          xcode-version: latest-stable
+          xcode-version: ${{ env.CommunityToolkitLibrary_Xcode_Version }}
 
       - name: Install Latest .NET SDK, v${{ env.LATEST_NET_VERSION }}
         uses: actions/setup-dotnet@v5