pip: bump prometheus-client from 0.11.0 to 0.13.1

Bumps [prometheus-client](https://github.com/prometheus/client_python) from 0.11.0 to 0.13.1.
- [Release notes](https://github.com/prometheus/client_python/releases)
- [Commits](prometheus/client_python@v0.11.0...v0.13.1)

---
updated-dependencies:
- dependency-name: prometheus-client
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

requirements.txt

@@ -2,6 +2,6 @@ Flask==2.0.2
 flask-healthz==0.0.3
 Flask-HTTPAuth==4.5.0
 gunicorn==20.1.0
-prometheus-client==0.11.0
+prometheus-client==0.13.1
 requests==2.27.1
 retry==0.9.2