Bump govuk_schemas from 4.2.0 to 4.3.0

Bumps [govuk_schemas](https://github.com/alphagov/govuk_schemas_gem) from 4.2.0 to 4.3.0.
- [Release notes](https://github.com/alphagov/govuk_schemas_gem/releases)
- [Changelog](https://github.com/alphagov/govuk_schemas/blob/master/CHANGELOG.md)
- [Commits](alphagov/govuk_schemas@v4.2.0...v4.3.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Gemfile.lock

@@ -117,7 +117,7 @@ GEM
       sentry-raven (~> 3.1.1)
       statsd-ruby (~> 1.5.0)
       unicorn (>= 5.4, < 5.9)
-    govuk_schemas (4.2.0)
+    govuk_schemas (4.3.0)
       json-schema (~> 2.8.0)
     govuk_test (2.0.0)
       brakeman (~> 4.6)