chore: bump flask from 3.1.0 to 3.1.3 in /examples/buildpacks-python (#10006)

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]

examples/buildpacks-python/requirements.txt

@@ -1 +1 @@
-Flask==3.1.0
+Flask==3.1.3