fix(deps): update dependency postcss-loader to v7 (#358)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package-lock.json

@@ -67,7 +67,7 @@
     "mini-css-extract-plugin": "1.6.2",
     "postcss": "8.4.23",
     "postcss-custom-media": "^9.1.2",
-    "postcss-loader": "6.2.1",
+    "postcss-loader": "7.3.0",
     "postcss-rtlcss": "3.7.2",
     "react-dev-utils": "12.0.1",
     "react-refresh": "0.14.0",