create-release-branch fails immediately when encountering a `patch:` dependency

[mcmire]

If the repo on which this tool is run has a dependency that uses the patch: protocol — this is common when using Yarn's patch feature — then the tool will fail immediately, without presenting the user with a spec. This happens because when parsing package.json we need to validate the shape of the manifest data. When we encounter dependencies we only allow npm: and workspace: dependencies and we reject the rest. We should investigate whether this is necessary and allow everything if possible.