Bump prometheus_exporter from 2.0.3 to 2.0.4

Bumps [prometheus_exporter](https://github.com/discourse/prometheus_exporter) from 2.0.3 to 2.0.4.
- [Release notes](https://github.com/discourse/prometheus_exporter/releases)
- [Changelog](https://github.com/discourse/prometheus_exporter/blob/main/CHANGELOG)
- [Commits](https://github.com/discourse/prometheus_exporter/compare/v2.0.3...v2.0.4)

---
updated-dependencies:
- dependency-name: prometheus_exporter
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -290,7 +290,7 @@ GEM
       ast (~> 2.4.1)
     path_expander (1.1.1)
     pg (1.4.4)
-    prometheus_exporter (2.0.3)
+    prometheus_exporter (2.0.4)
       webrick
     pry (0.14.1)
       coderay (~> 1.1)