in fails if release tag points to another tag

[aoldershaw]

GitHub releases can reference an annotated tag, which is a git object that points to another git object. Currently, we assume that the annotated tag points to a commit:

https://github.com/concourse/github-release-resource/blob/af189e098cf29692d719da181a47395ef1ac0843/github.go#L298-L309

However, an annotated tag can point to another annotated tag (which then points to a commit), which is a case we don't handle. In general, there could be an arbitrarily long chain of tags before resolving to a commit.

example problematic release - https://github.com/opencontainers/runc/releases/tag/v1.0.0-rc90