Build(deps): Bump the uv group across 1 directory with 2 updates (#225)

Bumps the uv group with 2 updates in the /backend directory: [nltk](https://github.com/nltk/nltk) and [pypdf](https://github.com/py-pdf/pypdf).


Updates `nltk` from 3.9.2 to 3.9.3
- [Changelog](https://github.com/nltk/nltk/blob/develop/ChangeLog)
- [Commits](nltk/nltk@3.9.2...3.9.3)

Updates `pypdf` from 6.7.1 to 6.7.3
- [Release notes](https://github.com/py-pdf/pypdf/releases)
- [Changelog](https://github.com/py-pdf/pypdf/blob/main/CHANGELOG.md)
- [Commits](py-pdf/pypdf@6.7.1...6.7.3)

---
updated-dependencies:
- dependency-name: nltk
  dependency-version: 3.9.3
  dependency-type: direct:production
  dependency-group: uv
- dependency-name: pypdf
  dependency-version: 6.7.3
  dependency-type: direct:production
  dependency-group: uv
...

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

Author: dependabot[bot]

backend/pyproject.toml

@@ -25,12 +25,12 @@ dependencies = [
     "markdown==3.8.2",
     "myst-parser==4.0.1",
     "nest-asyncio>=1.6.0",
-    "nltk==3.9.2",
+    "nltk==3.9.3",
     "openai==1.100.2",
     "protobuf>=5.29.6",
     "psycopg2-binary>=2.9.11",
     "pydantic>=2.11.7",
-    "pypdf==6.7.1",
+    "pypdf==6.7.3",
     "rank-bm25==0.2.2",
     "rich>=13.7.0",
     "sentence-transformers>=5.1.0",