chore: attach mongoMemoryServer to db and destroy in tests (#5326)

* chore: attach mongoMemoryServer to db and destroy in tests

* bump mongodb-memory-server to 9.x

---------

Co-authored-by: Paul Popus <paul@nouance.io>

test/plugin-nested-docs/int.spec.ts

@@ -1,9 +1,5 @@
-import type {
-  ArrayField,
-  RelationshipField,
-} from '../../packages/payload/src/fields/config/types.js'
+import type { ArrayField, RelationshipField, } from '../../packages/payload/src/fields/config/types.js'
 import type { Payload } from '../../packages/payload/src/index.js'
-
 import { getPayload } from '../../packages/payload/src/index.js'
 import { startMemoryDB } from '../startMemoryDB.js'
 import configPromise from './config.js'
@@ -16,6 +12,12 @@ describe('@payloadcms/plugin-nested-docs', () => {
     payload = await getPayload({ config })
   })
 
+  afterAll(async () => {
+    if (typeof payload.db.destroy === 'function') {
+      await payload.db.destroy()
+    }
+  })
+
   describe('seed', () => {
     it('should populate two levels of breadcrumbs', async () => {
       const query = await payload.find({