Bump clean-css from 4.1.8 to 4.2.3

Bumps [clean-css](https://github.com/jakubpawlowicz/clean-css) from 4.1.8 to 4.2.3.
- [Release notes](https://github.com/jakubpawlowicz/clean-css/releases)
- [Changelog](https://github.com/jakubpawlowicz/clean-css/blob/v4.2.3/History.md)
- [Commits](https://github.com/jakubpawlowicz/clean-css/compare/v4.1.8...v4.2.3

)

Signed-off-by: dependabot[bot] <support@github.com>

package-lock.json

@@ -4030,9 +4030,9 @@
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     },
     "clean-css": {
-      "version": "4.2.2",
-      "resolved": "https://registry.npmjs.org/clean-css/-/clean-css-4.2.2.tgz",
-      "integrity": "sha512-yKycArwReQXbOD/3pmsPmt6p7oUBww8MisDabL2pCUWkbVONvCJoBdCjgY4ZVQmKX5juz/JB9oDcP6XzGUpjwQ==",
+      "version": "4.2.3",
+      "resolved": "https://registry.npmjs.org/clean-css/-/clean-css-4.2.3.tgz",
+      "integrity": "sha512-VcMWDN54ZN/DS+g58HYL5/n4Zrqe8vHJpGA8KdgUXFU4fuP/aHNw8eld9SyEIyabIMJX/0RaY/fplOo5hYLSFA==",
       "requires": {
         "source-map": "~0.6.0"
       },