workflow: switch to pnpm

Author: yyx990803

package.json

@@ -75,14 +75,12 @@
     "markdown-loader": "^2.0.2",
     "memfs": "^3.1.2",
     "mini-css-extract-plugin": "^0.4.1",
-    "node-sass": "^4.7.2",
     "normalize-newline": "^3.0.0",
     "null-loader": "^0.1.1",
     "postcss-loader": "^2.1.2",
     "pug": "^2.0.1",
     "pug-plain-loader": "^1.0.0",
     "raw-loader": "^0.5.1",
-    "sass-loader": "^6.0.7",
     "source-map": "^0.5.0",
     "stylus": "^0.54.5",
     "stylus-loader": "^3.0.2",