Update the parser regex of map_rerank (#6419)

Sometimes the score responded by chatgpt would be like 'Respone
example\nScore: 90 (fully answers the question, but could provide more
detail on the specific error message)'
For the score contains not only numbers, it raise a ValueError like 


Update the RegexParser from `.*` to `\d*` would help us to ignore the
text after number.

Co-authored-by: Bagatur <baskaryan@gmail.com>

langchain/chains/question_answering/map_rerank_prompt.py

@@ -3,7 +3,7 @@ from langchain.output_parsers.regex import RegexParser
 from langchain.prompts import PromptTemplate
 
 output_parser = RegexParser(
-    regex=r"(.*?)\nScore: (.*)",
+    regex=r"(.*?)\nScore: (\d*)",
     output_keys=["answer", "score"],
 )
 

tests/unit_tests/chains/question_answering/test_map_rerank_prompt.py

@@ -0,0 +1,17 @@
+"""Test map_rerank parser"""
+import pytest
+
+from langchain.chains.question_answering.map_rerank_prompt import output_parser
+
+GOOD_SCORE = "foo bar answer.\nScore: 80"
+SCORE_WITH_EXPLANATION = "foo bar answer.\nScore: 80 (fully answers the question, but could provide more detail on the specific error message)"  # noqa: E501
+
+
+@pytest.mark.parametrize("answer", (GOOD_SCORE, SCORE_WITH_EXPLANATION))
+def test_parse_scores(answer: str) -> None:
+    result = output_parser.parse(answer)
+
+    assert result["answer"] == "foo bar answer."
+
+    score = int(result["score"])
+    assert score == 80