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] <support@github.com>

Gemfile.lock

@@ -203,7 +203,7 @@ GEM
       rinku (~> 2.0)
       sanitize (~> 6)
     govuk_ab_testing (3.0.0)
-    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)
@@ -319,7 +319,7 @@ GEM
       net-protocol
     netrc (0.11.0)
     nio4r (2.7.4)
-    nokogiri (1.16.8)
+    nokogiri (1.17.1)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
     null_logger (0.0.1)