fix(tests): update expected message in AiProviderServiceTest

Updated the expected response message in the AiProviderServiceTest to match the correct phrasing of the joke.

tests/Feature/Service/AiProviderServiceTest.php

@@ -109,7 +109,7 @@ public function test_prompt_sends_correct_request()
             'Tell me a joke.'
         );
 
-        $this->assertEquals(['message' => "Why don't scientists trust at...thing!"], $response);
+        $this->assertEquals(['message' => "Why don't scientists trust atoms? Because they make up everything!"], $response);
     }
 
     public function test_prompt_with_pictures_handles_transcoding_failure()