Fix collection attribute typing

tests/Console/ModelsCommand/GenerateMixinCollection/Models/WithCollection.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace Barryvdh\LaravelIdeHelper\Tests\Console\ModelsCommand\GenerateMixinCollection\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Support\Collection;
+
+class WithCollection extends Model
+{
+    /**
+     * @return Collection<int, string>
+     */
+    public function getCollectionAttribute(): Collection
+    {
+        return new Collection();
+    }
+
+    /**
+     * @return Collection
+     */
+    public function getCollectionWithoutTemplateAttribute(): Collection
+    {
+        return new Collection();
+    }
+
+    public function getCollectionWithoutDocBlockAttribute(): Collection
+    {
+        return new Collection();
+    }
+}