test: bump GeminiApiIntegrationTest to gemini-flash-latest

gemini-2.0-flash has been retired and returns HTTP 404, so the live Gemini
API integration test always failed. Use the gemini-flash-latest alias
instead.

PiperOrigin-RevId: 943725263

Author: damianmomotgoogle

contrib/spring-ai/src/test/java/com/google/adk/models/springai/integrations/GeminiApiIntegrationTest.java

@@ -48,7 +48,7 @@
 @EnabledIfEnvironmentVariable(named = "GOOGLE_API_KEY", matches = "\\S+")
 class GeminiApiIntegrationTest {
 
-  private static final String GEMINI_MODEL = "gemini-2.0-flash";
+  private static final String GEMINI_MODEL = "gemini-flash-latest";
 
   @Test
   void testSimpleAgentWithRealGeminiApi() throws InterruptedException {