Bump govuk_app_config from 1.15.0 to 1.15.1
Bump govuk_app_config from 1.15.0 to 1.15.1

Bumps [govuk_app_config](https://github.com/alphagov/govuk_app_config) from 1.15.0 to 1.15.1.
- [Release notes](https://github.com/alphagov/govuk_app_config/releases)
- [Changelog](https://github.com/alphagov/govuk_app_config/blob/master/CHANGELOG.md)
- [Commits](https://github.com/alphagov/govuk_app_config/compare/v1.15.0...v1.15.1)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
alphagov/smart-answers,alphagov/smart-answers,alphagov/smart-answers,alphagov/smart-answers