Bump flask in /circleci/images/citusupgradetester/files/etc

Bumps [flask](https://github.com/pallets/flask) from 3.1.2 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@3.1.2...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>

Author: dependabot[bot]

circleci/images/citusupgradetester/files/etc/requirements.txt

@@ -19,7 +19,7 @@ cryptography==46.0.5; python_version >= '3.8' and python_full_version not in '3.
 docopt==0.6.2
 execnet==2.1.2; python_version >= '3.8'
 filelock==3.25.0; python_version >= '3.10'
-flask==3.1.2; python_version >= '3.9'
+flask==3.1.3; python_version >= '3.9'
 h11==0.16.0; python_version >= '3.8'
 h2==4.3.0; python_version >= '3.9'
 hpack==4.1.0; python_version >= '3.9'