build(deps): bump newrelic_rpm from 9.20.0 to 9.21.0

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]>

Author: dependabot[bot]

Gemfile.lock

@@ -343,7 +343,7 @@ GEM
     net-ssh (7.3.0)
     netaddr (2.0.6)
     netrc (0.11.0)
-    newrelic_rpm (9.20.0)
+    newrelic_rpm (9.21.0)
     nio4r (2.7.4)
     nokogiri (1.18.9)
       mini_portile2 (~> 2.8.2)