Bump gulp-postcss to 10.0.0 (#4835)

Bumps [gulp-postcss](https://github.com/postcss/gulp-postcss) from 9.1.0 to 10.0.0.
- [Release notes](https://github.com/postcss/gulp-postcss/releases)
- [Commits](https://github.com/postcss/gulp-postcss/compare/9.1.0...10.0.0)

---
updated-dependencies:
- dependency-name: gulp-postcss
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

{{cookiecutter.project_slug}}/package.json

@@ -16,7 +16,7 @@
     "gulp": "^4.0.2",
     "gulp-imagemin": "^7.1.0",
     "gulp-plumber": "^1.2.1",
-    "gulp-postcss": "^9.0.1",
+    "gulp-postcss": "^10.0.0",
     "gulp-rename": "^2.0.0",
     "gulp-sass": "^5.0.0",
     "gulp-uglify-es": "^3.0.0",