`--dry-run` does not error for imports/exports problems

[nzakas]

I just ran into a couple of issues with --dry-run passed and then publish failed.

In the first case, there was an export that didn't exist:

{
   "name": "@scope/name",
   "version": "0.1.0",
   "exports": "./non-existent.ts"
}

In the second case, publish refused to follow imports outside of the project root:

{
   "name": "@scope/name",
   "version": "0.1.0",
   "exports": "./mod.ts",
   "imports": {
      "foo": "../bar.js"
   }
}

Both cases passed --dry-run, which makes me think that --dry-run doesn't read exports or imports.