chore(deps): update dependency postcss to v8.4.0 (#1075)

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/frontend/pulls/1075
Co-authored-by: renovate <renovatebot@kolaente.de>
Co-committed-by: renovate <renovatebot@kolaente.de>

package.json

@@ -64,6 +64,7 @@
     "@vitejs/plugin-legacy": "1.6.3",
     "@vitejs/plugin-vue": "1.10.0",
     "@vue/eslint-config-typescript": "9.1.0",
+    "autoprefixer": "^10.4.0",
     "axios": "0.24.0",
     "browserslist": "4.18.1",
     "cypress": "8.7.0",
@@ -75,7 +76,7 @@
     "faker": "5.5.3",
     "jest": "27.3.1",
     "netlify-cli": "8.0.0",
-    "postcss": "8.3.11",
+    "postcss": "8.4.0",
     "postcss-preset-env": "7.0.1",
     "rollup": "2.60.1",
     "rollup-plugin-visualizer": "5.5.2",