fix: Fixes a bug introduced by the underlying google genai library

We need to set project and location parameters when we instantiate the Google GenAI library Client for VertexAi. This used to work before through environment variables but it doesn't seem to work anymore. So we are updating the `ApigeeLlm` wrapper to read from `GOOGLE_CLOUD_PROJECT` and `GOOGLE_CLOUD_LOCATION` environment variables and pass to the Client constructor.

PiperOrigin-RevId: 829569362

src/google/adk/models/apigee_llm.py

@@ -37,6 +37,8 @@ logger = logging.getLogger('google_adk.' + __name__)
 
 _APIGEE_PROXY_URL_ENV_VARIABLE_NAME = 'APIGEE_PROXY_URL'
 _GOOGLE_GENAI_USE_VERTEXAI_ENV_VARIABLE_NAME = 'GOOGLE_GENAI_USE_VERTEXAI'
+_PROJECT_ENV_VARIABLE_NAME = 'GOOGLE_CLOUD_PROJECT'
+_LOCATION_ENV_VARIABLE_NAME = 'GOOGLE_CLOUD_LOCATION'
 
 
 class ApigeeLlm(Gemini):
@@ -90,6 +92,24 @@ class ApigeeLlm(Gemini):
       raise ValueError(f'Invalid model string: {model}')
 
     self._isvertexai = _identify_vertexai(model)
+
+    # Set the project and location for Vertex AI.
+    if self._isvertexai:
+      self._project = os.environ.get(_PROJECT_ENV_VARIABLE_NAME)
+      self._location = os.environ.get(_LOCATION_ENV_VARIABLE_NAME)
+
+      if not self._project:
+        raise ValueError(
+            f'The {_PROJECT_ENV_VARIABLE_NAME} environment variable must be'
+            ' set.'
+        )
+
+      if not self._location:
+        raise ValueError(
+            f'The {_LOCATION_ENV_VARIABLE_NAME} environment variable must be'
+            ' set.'
+        )
+
     self._api_version = _identify_api_version(model)
     self._proxy_url = proxy_url or os.environ.get(
         _APIGEE_PROXY_URL_ENV_VARIABLE_NAME
@@ -128,9 +148,15 @@ class ApigeeLlm(Gemini):
         **kwargs_for_http_options,
     )
 
+    kwargs_for_client = {}
+    kwargs_for_client['vertexai'] = self._isvertexai
+    if self._isvertexai:
+      kwargs_for_client['project'] = self._project
+      kwargs_for_client['location'] = self._location
+
     return Client(
-        vertexai=self._isvertexai,
         http_options=http_options,
+        **kwargs_for_client,
     )
 
   @override