Support str response type in Langchain

[hmstepanek]

Overview

Fix issue with Langchain where response is type string and only the first character is captured.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ ACTION	actionlint	4		0	0	0.43s
✅ MARKDOWN	markdownlint	7	0	0	0	0.96s
✅ MARKDOWN	markdown-link-check	7		0	0	16.8s
✅ PYTHON	ruff	893	0	0	0	0.5s
✅ PYTHON	ruff-format	893	0	0	0	0.28s
✅ YAML	prettier	10	0	0	0	0.97s
✅ YAML	v8r	10		0	0	4.79s
✅ YAML	yamllint	10		0	0	0.51s

See detailed report in MegaLinter reports

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 81.47%. Comparing base (0c59fe3) to head (21a82c5).

Files with missing lines	Patch %	Lines
newrelic/hooks/mlmodel_langchain.py	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1333      +/-   ##
==========================================
- Coverage   81.48%   81.47%   -0.01%     
==========================================
  Files         204      204              
  Lines       22821    22823       +2     
  Branches     3617     3618       +1     
==========================================
  Hits        18595    18595              
- Misses       3013     3016       +3     
+ Partials     1213     1212       -1     

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