Bump postcss from 8.5.6 to 8.5.12 in /extensions/copilot (#312410)

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.6 to 8.5.12.
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.5.6...8.5.12)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.10
  dependency-type: indirect
...

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

extensions/copilot/package-lock.json

@@ -18293,9 +18293,9 @@
 			}
 		},
 		"node_modules/postcss": {
-			"version": "8.5.6",
-			"resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.6.tgz",
-			"integrity": "sha512-3Ybi1tAuwAP9s0r1UQ2J4n5Y0G05bJkpUIO0/bI9MhwmD70S5aTWbXGBwxHrelT+XM1k6dM0pk+SwNkpTRN7Pg==",
+			"version": "8.5.12",
+			"resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.12.tgz",
+			"integrity": "sha512-W62t/Se6rA0Az3DfCL0AqJwXuKwBeYg6nOaIgzP+xZ7N5BFCI7DYi1qs6ygUYT6rvfi6t9k65UMLJC+PHZpDAA==",
 			"dev": true,
 			"funding": [
 				{