Bump flask in /samples/web-app-cosmosdb-nosql-api/python/src (#85)

Bumps [flask](https://github.com/pallets/flask) from 3.1.0 to 3.1.3.
- [Release notes](https://github.com/pallets/flask/releases)
- [Changelog](https://github.com/pallets/flask/blob/main/CHANGES.rst)
- [Commits](pallets/flask@3.1.0...3.1.3)

---
updated-dependencies:
- dependency-name: flask
  dependency-version: 3.1.3
  dependency-type: direct:production
...

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Author: dependabot[bot]

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

@@ -1,4 +1,4 @@
-Flask==3.1.0
+Flask==3.1.3
 azure-mgmt-cosmosdb==9.8.0
 azure-cosmos==4.7.0
 gunicorn==20.1.0