changed embedding model to `text-embedding-004`

app.py

@@ -25,7 +25,7 @@ def is_valid_gemini_api_key(api_key):
 def prepare_query_engine(api_key):
   # Gemini Embeddings
   embed_model = GeminiEmbedding(
-      model="models/embedding-004",
+      model="models/text-embedding-004",
       title="wikipedia page of the 'Oppenheimer' movie",
       embed_batch_size=16,
       api_key=api_key