Avoid having to install imagemagick and improve debug output

.github/workflows/map-diff.yml

@@ -15,7 +15,10 @@ jobs:
       run:
         working-directory: utils/wesnoth-map-diff
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
+      env:
+        _debug: ${{ toJSON(github) }}
+
     - uses: actions/setup-node@v3
       with:
         node-version: '16'
@@ -28,7 +31,7 @@ jobs:
       env:
         SHA: ${{ github.event.pull_request.head.sha }}
       run: |
-        sudo apt-get -y -q install pngquant imagemagick
+        sudo apt-get -y -q install pngquant
         comment_body=""
         log() { printf '\e[1m%s\e[m\n' "$*"; } # write log message in bold
         err() { printf '\e[1;31m%s\e[m\n' "$*"; exit 1; } # write error message in bold red and exit
@@ -49,11 +52,9 @@ jobs:
 
           log "Generate map diff image for $map_path..."
           node build/index.js "../../$map_path" "$new_map" diff_image.png
-          identify diff_image.png
 
           log 'Compress image...'
-          pngquant --force --output diff_image.png diff_image.png
-          identify diff_image.png
+          pngquant --verbose --force --output diff_image.png diff_image.png
 
           log 'Uploading diff_image.png...'
           # https://api.imgur.com/endpoints/image/#image-upload https://apidocs.imgur.com/#c85c9dfc-7487-4de2-9ecd-66f727cf3139
@@ -63,7 +64,7 @@ jobs:
           # careful with leading spaces in the output since it is ultimately markdown (with embedded html) so the indentation may have meaning
           html=$(printf %s "$json" | jq -rRs --arg path "$map_path" --arg dim "$old_dim ➔ $new_dim" '. as $input |
             try fromjson catch ({error:$input}) | (if .data.link then "map diff image" else "image upload failed" end) as $alt |
-            @html "<h3>\($path)</h3><p>dimensions: \($dim)</p><img src=\"\(.data.link)\" alt=\"\($alt)\"/><br/><details><summary>imgur response</summary><p>\(tojson)</p></details>"')
+            @html "<h3>\($path)</h3><p>dimensions: \($dim)</p><img src=\"\(.data.link)\" alt=\"\($alt)\"/><br/><details><summary>imgur response</summary><p>\n\n```json", ., "```\n</p></details>"')
           comment_body+=$html$'\n'
         done