getTag method
Fetches a tag from the repo given a SHA.
API docs: https://developer.github.com/v3/git/tags/#get-a-tag
Implementation
Future<GitTag> getTag(RepositorySlug slug, String? sha) =>
github.getJSON('/repos/${slug.fullName}/git/tags/$sha',
convert: GitTag.fromJson, statusCode: StatusCodes.OK);