Bump prometheus-client from 4.1.0 to 4.2.1

Bumps [prometheus-client](https://github.com/prometheus/client_ruby) from 4.1.0 to 4.2.1.
- [Release notes](https://github.com/prometheus/client_ruby/releases)
- [Changelog](https://github.com/prometheus/client_ruby/blob/main/CHANGELOG.md)
- [Commits](prometheus/client_ruby@v4.1.0...v4.2.1)

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

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

Gemfile.lock

@@ -14,7 +14,7 @@ GEM
     octokit (6.1.0)
       faraday (>= 1, < 3)
       sawyer (~> 0.9)
-    prometheus-client (4.1.0)
+    prometheus-client (4.2.1)
     public_suffix (5.0.1)
     rake (13.0.6)
     rexml (3.2.5)