Bump langchain from 1.2.13 to 1.2.15 (#395)

Bumps [langchain](https://github.com/langchain-ai/langchain) from 1.2.13 to 1.2.15.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain==1.2.13...langchain==1.2.15)

---
updated-dependencies:
- dependency-name: langchain
  dependency-version: 1.2.15
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

AI-Travel-Agent/requirements.txt

@@ -1,7 +1,7 @@
 amadeus==12.0.0
 ipykernel==7.2.0
 jupyter==1.1.1
-langchain==1.2.13
+langchain==1.2.15
 langchain-community==0.4.1
 streamlit==1.55.0
 huggingface-hub==1.9.0

Text-Summarizer-Browser-Plugin/requirements.txt

@@ -1,6 +1,6 @@
 flask==3.1.3
 flask_cors==6.0.2
-langchain==1.2.13
+langchain==1.2.15
 langchain-community==0.4.1
 sentence-transformers==5.3.0
 langchain_chroma==1.1.0