Bump flask in /samples/web-app-managed-identity/python/src (#88)

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
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Paolo Salvatori <leprino@hotmail.com>

Author: dependabot[bot]

samples/web-app-managed-identity/python/src/requirements.txt

@@ -1,4 +1,4 @@
-Flask==3.1.0
+Flask==3.1.3
 azure-identity==1.16.1
 azure-storage-blob==12.26.0
 azure-core==1.38.0