`Rails::SourceAnnotationExtractor::Annotation.tags` may be modified by
app configuration.  Therefore, resolve default annotation tags after
loading the app configuration.

This fixes errors like https://buildkite.com/rails/rails/builds/74268#240d60bc-baa7-4b6e-ad21-b3172095f939/1083-1092
resulting from erikhuda/thor@0222fe52ed3803fe3ee0033da5b6faac5ee6299c.