build(🧶): bump storybook to 6.5 alpha

fix: pin `autoprefixer`

meant to avoid:

```sh
...
Error: PostCSS plugin autoprefixer requires PostCSS 8.
...
```

redwoodjs#3515 (comment)
parcel-bundler/parcel#5160

chore: test using `yarn`'s `resolutions`

see: https://stackoverflow.com/a/66825007

__fixtures__/test-project/web/package.json

@@ -26,5 +26,10 @@
     "postcss": "^8.4.7",
     "postcss-loader": "^6.2.1",
     "tailwindcss": "^3.0.23"
+  },
+  "resolutions": {
+    "autoprefixer": "^10.4.2",
+    "postcss": "^8.4.7",
+    "postcss-loader": "^6.2.1"
   }
 }

packages/testing/package.json

@@ -31,10 +31,10 @@
     "@redwoodjs/internal": "0.47.0",
     "@redwoodjs/router": "0.47.0",
     "@redwoodjs/web": "0.47.0",
-    "@storybook/addon-a11y": "6.4.19",
-    "@storybook/builder-webpack5": "6.4.19",
-    "@storybook/manager-webpack5": "6.4.19",
-    "@storybook/react": "6.4.19",
+    "@storybook/addon-a11y": "6.5.0-alpha.42",
+    "@storybook/builder-webpack5": "6.5.0-alpha.42",
+    "@storybook/manager-webpack5": "6.5.0-alpha.42",
+    "@storybook/react": "6.5.0-alpha.42",
     "@testing-library/jest-dom": "5.16.2",
     "@testing-library/react": "12.1.3",
     "@testing-library/user-event": "13.5.0",