chore(deps): update dependency langchain-google-vertexai to v2.1.2 (#339)

Author: renovate-bot

samples/index_tuning_sample/requirements.txt

@@ -1,3 +1,3 @@
 langchain-community==0.3.29
 langchain-google-cloud-sql-pg==0.14.1
-langchain-google-vertexai==2.0.28
+langchain-google-vertexai==2.1.2