[5.x] Fix structure not being saved to collection (#13479)

Author: jasonvarga

src/Entries/Collection.php

@@ -482,6 +482,8 @@ public function save()
     {
         $isNew = ! Facades\Collection::handleExists($this->handle);
 
+        Blink::forget("collection-{$this->id()}-structure");
+
         $withEvents = $this->withEvents;
         $this->withEvents = true;
 

tests/Data/Entries/CollectionTest.php

@@ -501,6 +501,7 @@ public function it_saves_the_collection_through_the_api()
 
         Facades\Collection::shouldReceive('save')->with($collection)->once();
         Facades\Collection::shouldReceive('handleExists')->with('test')->once();
+        Facades\Blink::shouldReceive('forget')->with('collection-test-structure')->once();
         Facades\Blink::shouldReceive('forget')->with('collection-handles')->once();
         Facades\Blink::shouldReceive('forget')->with('mounted-collections')->once();
         Facades\Blink::shouldReceive('flushStartingWith')->with('collection-test')->once();