[tests] Try building with ENABLE_VC_BUILD (vercel#8110)

This will dogfood `vc build` which happens to improve this deployment time from 4 min down to 2 min.

Author: styfle

api/package.json

@@ -5,7 +5,8 @@
   "description": "API for the vercel/vercel repo",
   "main": "index.js",
   "scripts": {
-    "vercel-build": "node ../utils/run.js build all"
+    "//TODO": "We should add this pkg to yarn workspaces",
+    "vercel-build": "cd .. && yarn install && yarn vercel-build"
   },
   "dependencies": {
     "@sentry/node": "5.11.1",

vercel.json

@@ -20,7 +20,7 @@
   ],
   "build": {
     "env": {
-      "ENABLE_FILE_SYSTEM_API": "1"
+      "ENABLE_VC_BUILD": "1"
     }
   },
   "github": {