Remove unrelated images from _site before deploying to preview repo

because the whole build result for 20 years of Rubima is too huge, and
most of the size is taken up by images.

Author: amatsuda

.github/workflows/preview.yml

@@ -34,6 +34,9 @@ jobs:
         env:
           JEKYLL_ENV: production
 
+      - name: Remove unrelated contents
+        run: git diff --name-only origin/master --relative=articles | ruby -nle 'puts $_[%r([0-9]{4}-[0-9]{2}-[0-9]{2}-([0-9]{4}-.+)\.md), 1]' | tr '\n' ',' | ruby -rfileutils -nle 'Dir.chdir("_site/images") { Dir.glob("*").each { FileUtils.rm_r(_1) if File.directory?(_1) && !$_.split(",").include?(_1) } }'
+
       - name: Deploy preview
         uses: rossjrw/pr-preview-action@v1
         with: