Bump notifications-ruby-client from 5.3.0 to 5.4.0

Bumps [notifications-ruby-client](https://github.com/alphagov/notifications-ruby-client) from 5.3.0 to 5.4.0.
- [Changelog](https://github.com/alphagov/notifications-ruby-client/blob/main/CHANGELOG.md)
- [Commits](alphagov/notifications-ruby-client@5.3.0...5.4.0)

---
updated-dependencies:
- dependency-name: notifications-ruby-client
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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

Gemfile.lock

@@ -303,7 +303,7 @@ GEM
       racc (~> 1.4)
     nokogiri (1.15.4-x86_64-linux)
       racc (~> 1.4)
-    notifications-ruby-client (5.3.0)
+    notifications-ruby-client (5.4.0)
       jwt (>= 1.5, < 3)
     null_logger (0.0.1)
     opentelemetry-api (1.2.3)