Bump govuk_app_config from 9.15.4 to 9.15.5

Bumps [govuk_app_config](https://github.com/alphagov/govuk_app_config) from 9.15.4 to 9.15.5.
- [Changelog](https://github.com/alphagov/govuk_app_config/blob/main/CHANGELOG.md)
- [Commits](alphagov/govuk_app_config@v9.15.4...v9.15.5)

---
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

@@ -242,7 +242,7 @@ GEM
       jquery-rails (~> 4.3)
       plek (>= 2.1)
       rails (>= 6)
-    govuk_app_config (9.15.4)
+    govuk_app_config (9.15.5)
       logstasher (~> 2.1)
       opentelemetry-exporter-otlp (>= 0.25, < 0.30)
       opentelemetry-instrumentation-all (>= 0.39.1, < 0.70.0)
@@ -403,14 +403,14 @@ GEM
       net-protocol
     netrc (0.11.0)
     nio4r (2.7.4)
-    nokogiri (1.17.0)
+    nokogiri (1.17.1)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
-    nokogiri (1.17.0-aarch64-linux)
+    nokogiri (1.17.1-aarch64-linux)
       racc (~> 1.4)
-    nokogiri (1.17.0-arm64-darwin)
+    nokogiri (1.17.1-arm64-darwin)
       racc (~> 1.4)
-    nokogiri (1.17.0-x86_64-linux)
+    nokogiri (1.17.1-x86_64-linux)
       racc (~> 1.4)
     notifications-ruby-client (6.0.0)
       jwt (>= 1.5, < 3)