Update dependency clean-css to v5

Author: renovate-bot

package.json

@@ -34,7 +34,7 @@
     "@11ty/eleventy-plugin-rss": "^1.1.1",
     "@tryghost/content-api": "^1.4.4",
     "@tryghost/helpers": "^1.1.6",
-    "clean-css": "^4.2.1",
+    "clean-css": "^5.0.0",
     "cross-env": "^7.0.0",
     "dotenv": "^8.0.0",
     "eleventy-plugin-lazyimages": "liamfiddler/eleventy-plugin-lazyimages",

yarn.lock

@@ -1021,6 +1021,13 @@ clean-css@^4.1.11, clean-css@^4.2.1:
   dependencies:
     source-map "~0.6.0"
 
+clean-css@^5.0.0:
+  version "5.1.2"
+  resolved "https://registry.yarnpkg.com/clean-css/-/clean-css-5.1.2.tgz#6ea0da7286b4ddc2469a1b776e2461a5007eed54"
+  integrity sha512-QcaGg9OuMo+0Ds933yLOY+gHPWbxhxqF0HDexmToPf8pczvmvZGYzd+QqWp9/mkucAOKViI+dSFOqoZIvXbeBw==
+  dependencies:
+    source-map "~0.6.0"
+
 clean-regexp@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/clean-regexp/-/clean-regexp-1.0.0.tgz#8df7c7aae51fd36874e8f8d05b9180bc11a3fed7"