Bump autoprefixer from 9.7.5 to 9.7.6 (#13467)

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 9.7.5 to 9.7.6.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/autoprefixer/compare/9.7.5...9.7.6)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

package.json

@@ -72,7 +72,7 @@
     "@rails/ujs": "^6.0.2",
     "array-includes": "^3.1.1",
     "arrow-key-navigation": "^1.1.0",
-    "autoprefixer": "^9.7.5",
+    "autoprefixer": "^9.7.6",
     "axios": "^0.19.2",
     "babel-loader": "^8.1.0",
     "babel-plugin-lodash": "^3.3.4",