Avoid running migrations in Vercel on PR branches

vercel.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+if [[ $VERCEL_ENV == "production"  ]] ; then 
+  pnpm run build && pnpm prisma migrate deploy
+else 
+  # prod and preview use the same database.
+  # We don't want to risk breaking it with a work-in-progress migration in a PR.
+  pnpm run build
+fi