Bump stylelint from 13.8.0 to 13.9.0 (#6641)

Bumps [stylelint](https://github.com/stylelint/stylelint) from 13.8.0 to 13.9.0.
- [Release notes](https://github.com/stylelint/stylelint/releases)
- [Changelog](https://github.com/stylelint/stylelint/blob/master/CHANGELOG.md)
- [Commits](stylelint/stylelint@13.8.0...13.9.0)

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

package.json

@@ -166,7 +166,7 @@
     "sass-loader": "10.1.1",
     "scss-bundle": "2.3.2",
     "selenium-webdriver": "4.0.0-alpha.7",
-    "stylelint": "^13.8.0",
+    "stylelint": "^13.9.0",
     "ts-node": "^9.0.0",
     "tsconfig-paths": "^3.9.0",
     "tslint": "6.1.3",