Bump prometheus-client from 0.17.1 to 0.21.1

Bumps [prometheus-client](https://github.com/prometheus/client_python) from 0.17.1 to 0.21.1.
- [Release notes](https://github.com/prometheus/client_python/releases)
- [Commits](prometheus/client_python@v0.17.1...v0.21.1)

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

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

requirements.txt

@@ -37,7 +37,7 @@ tabulate==0.9.0
 zipstream-new==1.1.8
 pika==1.3.2
 sentry-sdk[flask]==2.10.0
-prometheus-client==0.17.1
+prometheus-client==0.21.1
 lxml==5.3.0
 lxml_html_clean==0.3.1
 pyicu==2.14