workflows/docker: fix publishing Docker images (again)

Follow-up to #19480. Tags were being serialised in the wrong format.
This fixes that.

.github/workflows/docker.yml

@@ -29,6 +29,7 @@ jobs:
       tags: ${{ steps.attributes.outputs.tags }}
       labels: ${{ steps.attributes.outputs.labels }}
       push: ${{ steps.attributes.outputs.push }}
+      merge: ${{ steps.attributes.outputs.merge }}
     steps:
       - name: Checkout
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
@@ -62,6 +63,7 @@ jobs:
           typeset -A tag_hash
           typeset -A push_hash
           matrix=()
+          merge=false
           while IFS=$'\n' read -r version; do
             tags=()
             if [[ "${GITHUB_EVENT_NAME}" == "release" ]]; then
@@ -91,8 +93,12 @@ jobs:
             fi
 
             if [[ "${#tags[@]}" -ne 0 ]]; then
-              tag_hash["${version}"]="${tags[*]}"
+              tags_as_json_array="$(
+                jq --null-input --compact-output '$ARGS.positional' --args "${tags[@]}"
+              )"
+              tag_hash["${version}"]="${tags_as_json_array}"
               push_hash["${version}"]=true
+              merge=true
               matrix+=("${version}")
             else
               push_hash["${version}"]=false
@@ -101,6 +107,7 @@ jobs:
 
           # Transform the `matrix` variable into a JSON array.
           echo "matrix=$(jq --null-input --compact-output '$ARGS.positional' --args "${matrix[@]}")" >>"${GITHUB_OUTPUT}"
+          echo "merge=${merge}" >>"${GITHUB_OUTPUT}"
 
           {
             DELIMITER="END_TAGS_$(uuidgen)"
@@ -109,7 +116,7 @@ jobs:
             printf '{'
             for version in "${!tag_hash[@]}"; do
               [[ -n "${has_previous:-}" ]] && printf ','
-              printf '"%s": "%s"' "${version}" "${tag_hash[$version]}"
+              printf '"%s": %s' "${version}" "${tag_hash[$version]}"
               has_previous=1
             done
             echo '}'
@@ -123,7 +130,7 @@ jobs:
             printf '{'
             for version in "${!push_hash[@]}"; do
               [[ -n "${has_previous:-}" ]] && printf ','
-              printf '"%s": "%s"' "${version}" "${push_hash[$version]}"
+              printf '"%s": %s' "${version}" "${push_hash[$version]}"
               has_previous=1
             done
             echo '}'
@@ -234,7 +241,7 @@ jobs:
 
   merge:
     needs: [generate-tags, build]
-    if: github.repository_owner == 'Homebrew'
+    if: github.repository_owner == 'Homebrew' && fromJSON(needs.generate-tags.outputs.merge)
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
@@ -266,22 +273,17 @@ jobs:
           username: BrewTestBot
           password: ${{ secrets.HOMEBREW_BREW_GITHUB_PACKAGES_TOKEN }}
 
-      - name: Export TAGS and VERSION to environment
+      - name: Merge and push Docker image
         env:
           TAGS: ${{ needs.generate-tags.outputs.tags }}
           VERSION: ${{ matrix.version }}
         run: |
-          filter="$(printf '.["%s"]' "${VERSION}")"
-          echo "TAGS=$(jq --raw-output "${filter}" <<<"${TAGS}")" >>"${GITHUB_ENV}"
-          echo "VERSION=${VERSION}" >>"${GITHUB_ENV}"
-
-      - name: Merge and push Docker image
-        run: |
+          filter="$(printf '.["%s"].[]' "${VERSION}")"
           tag_args=()
           while IFS=$'\n' read -r tag; do
             [[ -n "${tag}" ]] || continue
             tag_args+=("--tag=${tag}")
-          done <<<"${TAGS}"
+          done <<<"$(jq --raw-output "${filter}" <<<"${TAGS}")"
 
           image_args=("ghcr.io/homebrew/ubuntu${VERSION}@sha256:$(<"${RUNNER_TEMP}/digests/${VERSION}-x86_64")")
           if [[ "${VERSION}" != 18.04 ]]; then