[test] Stop opening browser by default in local Dev Overlay Storybook

This doesn't properly work with if a different Chrome release channel is used.
It's also annoying if you restart it and have a tab already open.
We don't open a browser in Next.js for those reasons.

Storybook includes a link to the local version in the terminal so you can always click that.

Author: eps1lon

packages/next/package.json

@@ -87,7 +87,7 @@
     "types": "tsc --project tsconfig.build.json --declaration --emitDeclarationOnly --stripInternal --declarationDir dist",
     "typescript": "tsec --noEmit",
     "ncc-compiled": "taskr ncc",
-    "storybook": "storybook dev -p 6006",
+    "storybook": "BROWSER=none storybook dev -p 6006",
     "build-storybook": "storybook build",
     "test-storybook": "test-storybook"
   },