build(deps): bump github.com/prometheus/client_golang (#2611)

Bumps [github.com/prometheus/client_golang](https://github.com/prometheus/client_golang) from 1.20.5 to 1.21.0.
- [Release notes](https://github.com/prometheus/client_golang/releases)
- [Changelog](https://github.com/prometheus/client_golang/blob/main/CHANGELOG.md)
- [Commits](https://github.com/prometheus/client_golang/compare/v1.20.5...v1.21.0

)

---
updated-dependencies:
- dependency-name: github.com/prometheus/client_golang
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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