Fix missing ' --allow-downgrade' switch on dotnet tool

Author: kzu

.github/workflows/build.yml

@@ -119,6 +119,13 @@ jobs:
           name: pkg
           path: bin
 
+      - name: ⚙ dotnet
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: |
+            8.x
+            9.x
+
       - name: 🚀 sleet
         env:
           SLEET_CONNECTION: ${{ secrets.SLEET_CONNECTION }}