Use JsonMockResponse instead of MockResponse in tests

Author: TomLisankie

src/platform/tests/Bridge/Anthropic/ModelClientTest.php

@@ -16,7 +16,7 @@
 use Symfony\AI\Platform\Bridge\Anthropic\Claude;
 use Symfony\AI\Platform\Bridge\Anthropic\ModelClient;
 use Symfony\Component\HttpClient\MockHttpClient;
-use Symfony\Component\HttpClient\Response\MockResponse;
+use Symfony\Component\HttpClient\Response\JsonMockResponse;
 
 #[CoversClass(ModelClient::class)]
 class ModelClientTest extends TestCase
@@ -53,7 +53,7 @@ public function testAnthropicBetaHeaderIsSetWithSingleBetaFeature(): void
             $this->assertArrayHasKey('anthropic-beta', $headers);
             $this->assertEquals('feature-1', $headers['anthropic-beta']);
 
-            return new MockResponse('{"success": true}');
+            return new JsonMockResponse('{"success": true}');
         });
 
         $this->modelClient = new ModelClient($this->httpClient, 'test-api-key');
@@ -70,7 +70,7 @@ public function testAnthropicBetaHeaderIsSetWithMultipleBetaFeatures(): void
             $this->assertArrayHasKey('anthropic-beta', $headers);
             $this->assertEquals('feature-1,feature-2,feature-3', $headers['anthropic-beta']);
 
-            return new MockResponse('{"success": true}');
+            return new JsonMockResponse('{"success": true}');
         });
 
         $this->modelClient = new ModelClient($this->httpClient, 'test-api-key', '2023-06-01');
@@ -86,7 +86,7 @@ public function testAnthropicBetaHeaderIsNotSetWhenBetaFeaturesIsEmpty(): void
 
             $this->assertArrayNotHasKey('anthropic-beta', $headers);
 
-            return new MockResponse('{"success": true}');
+            return new JsonMockResponse('{"success": true}');
         });
 
         $this->modelClient = new ModelClient($this->httpClient, 'test-api-key', '2023-06-01');
@@ -102,7 +102,7 @@ public function testAnthropicBetaHeaderIsNotSetWhenBetaFeaturesIsNotProvided():
 
             $this->assertArrayNotHasKey('anthropic-beta', $headers);
 
-            return new MockResponse('{"success": true}');
+            return new JsonMockResponse('{"success": true}');
         });
 
         $this->modelClient = new ModelClient($this->httpClient, 'test-api-key', '2023-06-01');