fix Prisma migrate

Author: dcousens

.changeset/fix-prisma-migrate.md

@@ -0,0 +1,5 @@
+---
+'@keystone-6/core': minor
+---
+
+Fix Prisma errors not showing when a Prisma migration errors internally

packages/core/src/lib/migrations.ts

@@ -1,4 +1,3 @@
-import { type ChildProcess } from 'node:child_process'
 import { toSchemasContainer } from '@prisma/internals'
 
 // @ts-expect-error
@@ -62,9 +61,9 @@ export async function withMigrate<T> (
       }
     })
   } finally {
-    const closePromise = new Promise<void>(resolve => {
-      const { child } = migrate.engine as { child: ChildProcess }
-      child.once('exit', () => resolve())
+    const closePromise = new Promise<void>(async (resolve) => {
+      await migrate.engine.initPromise
+      migrate.engine.child.once('exit', () => resolve())
     })
     migrate.stop()
     await closePromise