pip(deps): 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

@@ -10,7 +10,7 @@ start = "gh_actions_exporter.main:start"
 [tool.poetry.dependencies]
 python = "^3.9"
 fastapi = "^0.112.2"
-prometheus-client = "^0.20.0"
+prometheus-client = "^0.21.0"
 uvicorn = { extras = ["standard"], version = "^0.30.6" }
 python-multipart = "^0.0.9"
 PyYAML = "^6.0"