Update requirements.txt

Author: dishaprakash

samples/requirements.txt

@@ -1,5 +1,5 @@
-google-cloud-aiplatform[reasoningengine,langchain]==1.109.0
+google-cloud-aiplatform[reasoningengine,langchain]==1.90.0
 google-cloud-resource-manager==1.14.2
-langchain-community==0.3.27
+langchain-community==0.3.26
 langchain-google-alloydb-pg==0.12.0
-langchain-google-vertexai==2.0.28
+langchain-google-vertexai==2.0.20