Bump postcss and gulp-autoprefixer

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependency [gulp-autoprefixer](https://github.com/sindresorhus/gulp-autoprefixer). These dependencies need to be updated together.


Updates `postcss` from 7.0.39 to 8.4.31
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@7.0.39...8.4.31)

Updates `gulp-autoprefixer` from 6.1.0 to 8.0.0
- [Release notes](https://github.com/sindresorhus/gulp-autoprefixer/releases)
- [Commits](sindresorhus/gulp-autoprefixer@v6.1.0...v8.0.0)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: gulp-autoprefixer
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -45,7 +45,7 @@
 		"@babel/preset-env": "^7.20.2",
 		"del": "^5.1.0",
 		"gulp": "^4.0.0",
-		"gulp-autoprefixer": "^6.0.0",
+		"gulp-autoprefixer": "^8.0.0",
 		"gulp-babel": "^8.0.0",
 		"gulp-chmod": "^3.0.0",
 		"gulp-clean-css": "^3.10.0",