Bump highlight.js from 9.15.9 to 9.18.5 in /admin

Bumps [highlight.js](https://github.com/highlightjs/highlight.js) from 9.15.9 to 9.18.5.
- [Release notes](https://github.com/highlightjs/highlight.js/releases)
- [Changelog](https://github.com/highlightjs/highlight.js/blob/9.18.5/CHANGES.md)
- [Commits](https://github.com/highlightjs/highlight.js/compare/9.15.9...9.18.5)

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

admin/yarn.lock

@@ -3918,9 +3918,9 @@ hex-color-regex@^1.1.0:
   integrity sha1-TAb8y0YC/iYCs8k9+C1+fb8aio4=
 
 highlight.js@^9.6.0:
-  version "9.15.9"
-  resolved "https://registry.npm.taobao.org/highlight.js/download/highlight.js-9.15.9.tgz#865257da1dbb4a58c4552d46c4b3854f77f0e6d5"
-  integrity sha1-hlJX2h27SljEVS1GxLOFT3fw5tU=
+  version "9.18.5"
+  resolved "https://registry.yarnpkg.com/highlight.js/-/highlight.js-9.18.5.tgz#d18a359867f378c138d6819edfc2a8acd5f29825"
+  integrity sha512-a5bFyofd/BHCX52/8i8uJkjr9DYwXIPnM/plwI6W7ezItLGqzt7X2G2nXuYSfsIJdkwwj/g9DG1LkcGJI/dDoA==
 
 hmac-drbg@^1.0.0:
   version "1.0.1"