Fix regression trying to save empty translations

After the change from #418 translations were always considered dirty

Author: rbngzlv

src/Translatable/Translatable.php

@@ -347,6 +347,7 @@ protected function isTranslationDirty(Model $translation): bool
     {
         $dirtyAttributes = $translation->getDirty();
         unset($dirtyAttributes[$this->getLocaleKey()]);
+        unset($dirtyAttributes[$this->getTranslationRelationKey()]);
 
         return count($dirtyAttributes) > 0;
     }

tests/TranslatableTest.php

@@ -763,6 +763,25 @@ public function empty_translated_attribute(): void
         self::assertNull($vegetable->name);
     }
 
+    #[Test]
+    public function empty_translations_are_not_saved(): void
+    {
+        $vegetable = new Vegetable();
+        $vegetable->fill([
+            'en' => [],
+            'de' => ['name' => 'Erbsen'],
+        ]);
+
+        $vegetable->save();
+
+        self::assertDatabaseHas('vegetable_translations', [
+            'locale' => 'de',
+            'name' => 'Erbsen',
+        ]);
+
+        self::assertDatabaseMissing('vegetable_translations', ['locale' => 'en']);
+    }
+
     #[Test]
     public function numeric_translated_attribute(): void
     {