ci(test-all): add set up dotnet step

Author: vojtechmares

.github/workflows/test-all.yml

@@ -10,6 +10,11 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
 
+      - name: Set up dotnet
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '9.0.x'
+
       - name: dotnet build
         run: dotnet build