Update dependency autoprefixer to v10.4.21 (#863)

Author: renovate-04-kbuild[bot]

package-lock.json

@@ -31,7 +31,7 @@
     "@octokit/rest": "20.1.2",
     "@ronilaukkarinen/gulp-stylelint": "^14.1.1",
     "asciidoctor": "3.0.4",
-    "autoprefixer": "10.4.20",
+    "autoprefixer": "10.4.21",
     "browser-pack-flat": "3.5.0",
     "browserify": "17.0.1",
     "core-js": "3.41.0",