Bump postcss from 8.5.9 to 8.5.12 in /docusaurus (#17392)

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.9 to 8.5.12.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.9...8.5.12)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.12
  dependency-type: indirect
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docusaurus/yarn.lock

@@ -7627,9 +7627,9 @@ postcss-zindex@^6.0.2:
   integrity sha512-5BxW9l1evPB/4ZIc+2GobEBoKC+h8gPGCMi+jxsYvd2x0mjq7wazk6DrP71pStqxE9Foxh5TVnonbWpFZzXaYg==
 
 postcss@^8.4.21, postcss@^8.4.24, postcss@^8.4.33, postcss@^8.5.4, postcss@^8.5.6:
-  version "8.5.9"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.5.9.tgz#f6ee9e0b94f0f19c97d2f172bfbd7fc71fe1cca4"
-  integrity sha512-7a70Nsot+EMX9fFU3064K/kdHWZqGVY+BADLyXc8Dfv+mTLLVl6JzJpPaCZ2kQL9gIJvKXSLMHhqdRRjwQeFtw==
+  version "8.5.12"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.5.12.tgz#cd0c0f667f7cb0521e2313234ea6e707a9ec1ddb"
+  integrity sha512-W62t/Se6rA0Az3DfCL0AqJwXuKwBeYg6nOaIgzP+xZ7N5BFCI7DYi1qs6ygUYT6rvfi6t9k65UMLJC+PHZpDAA==
   dependencies:
     nanoid "^3.3.11"
     picocolors "^1.1.1"