Bump prometheus-client from 2.1.0 to 4.0.0

Bumps [prometheus-client](https://github.com/prometheus/client_ruby) from 2.1.0 to 4.0.0.
- [Release notes](https://github.com/prometheus/client_ruby/releases)
- [Changelog](https://github.com/prometheus/client_ruby/blob/master/CHANGELOG.md)
- [Commits](prometheus/client_ruby@v2.1.0...v4.0.0)

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

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

Gemfile

@@ -7,7 +7,7 @@ gem 'json',              '~> 2.3'
 gem 'net-smtp',          '~> 0.3.3'
 gem 'passenger',         '~> 6.0'
 gem 'pony',              '~> 1.13'
-gem 'prometheus-client', '~> 2.1'
+gem 'prometheus-client', '~> 4.0'
 gem 'rack',              '~> 2.2'
 gem 'sinatra',           '~> 2.1'
 

Gemfile.lock

@@ -28,7 +28,7 @@ GEM
       rake (>= 0.8.1)
     pony (1.13.1)
       mail (>= 2.0)
-    prometheus-client (2.1.0)
+    prometheus-client (4.0.0)
     rack (2.2.4)
     rack-protection (2.2.2)
       rack
@@ -77,7 +77,7 @@ DEPENDENCIES
   net-smtp (~> 0.3.3)
   passenger (~> 6.0)
   pony (~> 1.13)
-  prometheus-client (~> 2.1)
+  prometheus-client (~> 4.0)
   rack (~> 2.2)
   rack-test (~> 2.0)
   rubocop (~> 1.44)