Bump govuk_app_config from 9.15.3 to 9.15.4

Bumps [govuk_app_config](https://github.com/alphagov/govuk_app_config) from 9.15.3 to 9.15.4.
- [Changelog](https://github.com/alphagov/govuk_app_config/blob/main/CHANGELOG.md)
- [Commits](alphagov/govuk_app_config@v9.15.3...v9.15.4)

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

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

Gemfile.lock

@@ -204,7 +204,7 @@ GEM
       nokogiri (~> 1.12)
       rinku (~> 2.0)
       sanitize (~> 6)
-    govuk_app_config (9.15.3)
+    govuk_app_config (9.15.4)
       logstasher (~> 2.1)
       opentelemetry-exporter-otlp (>= 0.25, < 0.30)
       opentelemetry-instrumentation-all (>= 0.39.1, < 0.70.0)
@@ -251,7 +251,7 @@ GEM
       domain_name (~> 0.5)
     i18n (1.14.6)
       concurrent-ruby (~> 1.0)
-    io-console (0.7.2)
+    io-console (0.8.0)
     irb (1.14.1)
       rdoc (>= 4.0.0)
       reline (>= 0.4.2)
@@ -550,7 +550,8 @@ GEM
     pry-byebug (3.10.1)
       byebug (~> 11.0)
       pry (>= 0.13, < 0.15)
-    psych (5.2.0)
+    psych (5.2.1)
+      date
       stringio
     public_suffix (6.0.1)
     puma (6.5.0)
@@ -612,7 +613,7 @@ GEM
     redis-client (0.22.2)
       connection_pool
     regexp_parser (2.9.2)
-    reline (0.5.11)
+    reline (0.5.12)
       io-console (~> 0.5)
     request_store (1.7.0)
       rack (>= 1.4)
@@ -754,7 +755,7 @@ GEM
       addressable (>= 2.8.0)
       crack (>= 0.3.2)
       hashdiff (>= 0.4.0, < 2.0.0)
-    webrick (1.9.0)
+    webrick (1.9.1)
     websocket (1.2.10)
     websocket-driver (0.7.6)
       websocket-extensions (>= 0.1.0)