Bump flask from 2.1.1 to 2.3.2 in /examples/flask

Bumps [flask](https://github.com/pallets/flask) from 2.1.1 to 2.3.2.
- [Release notes](https://github.com/pallets/flask/releases)
- [Changelog](https://github.com/pallets/flask/blob/main/CHANGES.rst)
- [Commits](pallets/flask@2.1.1...2.3.2)

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

Signed-off-by: dependabot[bot] <support@github.com>

examples/flask/requirements.txt

@@ -1,4 +1,4 @@
-Flask==2.1.1
+Flask==2.3.2
 Flask-SQLAlchemy
 blinker
 pybrake