fix image reference "lost in translation"

Author: josephlukefahr

.github/workflows/artifact_validation.yaml

@@ -28,7 +28,7 @@ jobs:
   acvts_validation:
     runs-on: ubuntu-latest
     # Is this an appropriate dotnet image?
-    container: mcr.microsoft.com/dotnet/sdk:net6.0/runtime
+    container: mcr.microsoft.com/dotnet/sdk:net6.0
     steps:
       - name: Checkout code
         uses: actions/checkout@v4