Bump govuk_app_config from 9.15.2 to 9.15.3

Bumps [govuk_app_config](https://github.com/alphagov/govuk_app_config) from 9.15.2 to 9.15.3.
- [Changelog](https://github.com/alphagov/govuk_app_config/blob/main/CHANGELOG.md)
- [Commits](alphagov/govuk_app_config@v9.15.2...v9.15.3)

---
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

@@ -132,7 +132,7 @@ GEM
       rest-client (~> 2.0)
     globalid (1.2.1)
       activesupport (>= 6.1)
-    google-protobuf (4.28.3)
+    google-protobuf (4.29.0)
       bigdecimal
       rake (>= 13)
     googleapis-common-protos-types (1.16.0)
@@ -148,7 +148,7 @@ GEM
       rinku (~> 2.0)
       sanitize (~> 6)
     govuk_ab_testing (3.0.0)
-    govuk_app_config (9.15.2)
+    govuk_app_config (9.15.3)
       logstasher (~> 2.1)
       opentelemetry-exporter-otlp (>= 0.25, < 0.30)
       opentelemetry-instrumentation-all (>= 0.39.1, < 0.70.0)