Only tag sandbox images with sha and latest

Author: drew

.github/workflows/build-sandboxes.yml

@@ -98,8 +98,6 @@ jobs:
           images: ${{ env.REGISTRY }}/${{ env.IMAGE_PREFIX }}/sandboxes/${{ matrix.sandbox }}
           tags: |
             type=sha,prefix=
-            type=ref,event=branch
-            type=ref,event=pr
             type=raw,value=latest,enable={{is_default_branch}}
 
       - name: Build and push