chore(deps): update dependency postcss-loader to v7

Author: renovate[bot]

package.json

@@ -143,7 +143,7 @@
     "electron-notarize": "^1.0.1",
     "jest": "^26.6.3",
     "nock": "^13.0.5",
-    "postcss-loader": "^4.1.0",
+    "postcss-loader": "^7.0.0",
     "prettier": "^2.8.8",
     "react-test-renderer": "=16.14.0",
     "style-loader": "^3.3.3",