Bump newrelic_rpm from 9.20.0 to 9.21.0 (#5420)

Bumps [newrelic_rpm](https://github.com/newrelic/newrelic-ruby-agent) from 9.20.0 to 9.21.0.
- [Release notes](https://github.com/newrelic/newrelic-ruby-agent/releases)
- [Changelog](https://github.com/newrelic/newrelic-ruby-agent/blob/dev/CHANGELOG.md)
- [Commits](newrelic/newrelic-ruby-agent@9.20.0...9.21.0)

---
updated-dependencies:
- dependency-name: newrelic_rpm
  dependency-version: 9.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Gemfile.lock

@@ -423,7 +423,7 @@ GEM
       timeout
     net-smtp (0.5.1)
       net-protocol
-    newrelic_rpm (9.20.0)
+    newrelic_rpm (9.21.0)
     nio4r (2.7.4)
     nokogiri (1.18.9-arm64-darwin)
       racc (~> 1.4)