Bump urllib3 from 1.26.19 to 2.6.0 in /sample-apps/flask

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.19 to 2.6.0.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.26.19...2.6.0)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-version: 2.6.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

sample-apps/flask/requirements.txt

@@ -4,7 +4,7 @@ chardet==5.2.0
 Flask==2.3.3
 idna==3.7
 requests==2.32.0
-urllib3==1.26.19
+urllib3==2.6.0
 Werkzeug==3.0.6
 flask-sqlalchemy==2.5.1
 SQLAlchemy==1.4