ci: create multi-arch manifest from digest files using loop to reference basenames

Replace printf-based expansion with a shell loop that emits
ghcr.io/<repo>/<name>@sha256:<basename> for each file in /tmp/digests.
This ensures the manifest uses the digest hashes (file basenames) and
avoids including full file paths or formatting issues when joining entries.

Signed-off-by: Aaron Wislang <aaron.wislang@microsoft.com>

Author: asw101

.github/workflows/build-devcontainer.yml

@@ -159,7 +159,7 @@ jobs:
         run: |
           docker buildx imagetools create \
             $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
-            $(printf 'ghcr.io/${{ github.repository }}/${{ steps.image-name.outputs.name }}@sha256:%s ' /tmp/digests/*)
+            $(for digest in /tmp/digests/*; do echo "ghcr.io/${{ github.repository }}/${{ steps.image-name.outputs.name }}@sha256:$(basename $digest)"; done)
         env:
           DOCKER_METADATA_OUTPUT_JSON: ${{ steps.meta.outputs.json }}