remove checkout

.github/workflows/reusable-docker-build.yaml

@@ -107,9 +107,10 @@ jobs:
       ghcr-tag: ${{ steps.ghcr-tag.outputs.tag }}
 
     steps:
-      -
-        name: Checkout
-        uses: actions/checkout@v3.3.0
+      # no need for manual checkout, per https://github.com/docker/build-push-action/#git-context
+      # -
+      #   name: Checkout
+      #   uses: actions/checkout@v3.3.0
       -
         # we need qemu and buildx so we can build multiple platforms later
         name: Set up QEMU