Bump prometheus-client from 0.20.0 to 0.21.0

Bumps [prometheus-client](https://github.com/prometheus/client_python) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/prometheus/client_python/releases)
- [Commits](prometheus/client_python@v0.20.0...v0.21.0)

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

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

pyproject.toml

@@ -101,7 +101,7 @@ agents = [
     "fastcore==1.7.4",
     "pydantic==2.8.2",
     "tenacity==9.0.0",
-    "prometheus-client==0.20.0",
+    "prometheus-client==0.21.0",
     "opentelemetry-distro==0.48b0",
     "opentelemetry-instrumentation-fastapi==0.48b0",
     "opentelemetry-instrumentation-logging==0.48b0",