convert the parameter 'text' to uppercase in the function 'parse' of the class BooleanOutputParser (#5397)

when the LLMs output 'yes|no'，BooleanOutputParser can parse it to
'True|False', fix the ValueError in parse().
<!--
when use the BooleanOutputParser in the chain_filter.py, the LLMs output
'yes|no'，the function 'parse' will throw ValueError。
-->

Fixes # (issue)
  #5396
  https://github.com/hwchase17/langchain/issues/5396

---------

Co-authored-by: gaofeng27692 <gaofeng27692@hundsun.com>

langchain/output_parsers/boolean.py

@@ -16,12 +16,12 @@ class BooleanOutputParser(BaseOutputParser[bool]):
 
         """
         cleaned_text = text.strip()
-        if cleaned_text not in (self.true_val, self.false_val):
+        if cleaned_text.upper() not in (self.true_val.upper(), self.false_val.upper()):
             raise ValueError(
                 f"BooleanOutputParser expected output value to either be "
                 f"{self.true_val} or {self.false_val}. Received {cleaned_text}."
             )
-        return cleaned_text == self.true_val
+        return cleaned_text.upper() == self.true_val.upper()
 
     @property
     def _type(self) -> str:

tests/unit_tests/output_parsers/test_boolean_parser.py

@@ -12,6 +12,14 @@ def test_boolean_output_parser_parse() -> None:
     result = parser.parse("NO")
     assert result is False
 
+    # Test valid input
+    result = parser.parse("yes")
+    assert result is True
+
+    # Test valid input
+    result = parser.parse("no")
+    assert result is False
+
     # Test invalid input
     try:
         parser.parse("INVALID")