test(laravel): use createOne() for the for() relation (#8718)

create() returns Collection|Model, which PHPStan rejects as a for()
argument.

Author: soyuka

src/Laravel/Tests/NullableBelongsToTest.php

@@ -69,7 +69,7 @@ public function testOmittingBelongsToKeepsIt(): void
 
     public function testPatchWithExplicitNullClearsMorphTo(): void
     {
-        $slot = TimeSlotFactory::new()->create();
+        $slot = TimeSlotFactory::new()->createOne();
         $note = NullableMorphNoteFactory::new()->for($slot, 'noteable')->create();
         $this->assertNotNull(NullableMorphNote::query()->sole()->noteable_id); // @phpstan-ignore-line