Bump pymongo in /samples/web-app-cosmosdb-mongodb-api/python/src (#147)

Bumps [pymongo](https://github.com/mongodb/mongo-python-driver) from 4.18.2 to 4.18.3.
- [Release notes](https://github.com/mongodb/mongo-python-driver/releases)
- [Changelog](https://github.com/mongodb/mongo-python-driver/blob/4.18.3/doc/changelog.rst)
- [Commits](mongodb/mongo-python-driver@4.18.2...4.18.3)

---
updated-dependencies:
- dependency-name: pymongo
  dependency-version: 4.18.3
  dependency-type: direct:production
...

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Author: dependabot[bot]

samples/web-app-cosmosdb-mongodb-api/python/src/requirements.txt

@@ -1,5 +1,5 @@
 Flask==3.1.3
 azure-identity==1.25.3
-pymongo==4.18.2
+pymongo==4.18.3
 gunicorn==26.0.0
 python-dotenv==1.2.2