fix code injection vuln (#11233)

- **Description:** Fix a code injection vuln by adding one more keyword
into the filtering list
  - **Issue:** N/A
  - **Dependencies:** N/A
  - **Tag maintainer:** 
  - **Twitter handle:**

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

libs/experimental/langchain_experimental/pal_chain/base.py

@@ -20,7 +20,7 @@ from langchain_experimental.pal_chain.colored_object_prompt import COLORED_OBJEC
 from langchain_experimental.pal_chain.math_prompt import MATH_PROMPT
 from langchain_experimental.pydantic_v1 import Extra, Field
 
-COMMAND_EXECUTION_FUNCTIONS = ["system", "exec", "execfile", "eval"]
+COMMAND_EXECUTION_FUNCTIONS = ["system", "exec", "execfile", "eval", "__import__"]
 
 
 class PALValidation: