Fix function name in VertexAI Gemini streaming test

Author: markpollack

models/spring-ai-vertex-ai-gemini/src/test/java/org/springframework/ai/vertexai/gemini/tool/VertexAiGeminiChatModelToolCallingIT.java

@@ -147,7 +147,7 @@ public void functionCallTestInferredOpenApiSchemaStream() {
 
 var promptOptions = VertexAiGeminiChatOptions.builder()
 .model(VertexAiGeminiChatModel.ChatModel.GEMINI_2_0_FLASH)
-.toolCallbacks(List.of(FunctionToolCallback.builder("getCurrentWeather", new MockWeatherService())
+.toolCallbacks(List.of(FunctionToolCallback.builder("get_current_weather", new MockWeatherService())
 .description("Get the current weather in a given location")
 .inputType(MockWeatherService.Request.class)
 .build()))