Support issue comment references

[kettanaito]

Right now, if an issue comment is being referenced in a pull request, Release fails to properly figure out the issue number behind it.

• Example of such a CI run

This manifests in 2 errors:

ERROR: Failed to extract the authors for the issue #NaN: GitHub API responded with 1 error(s): [{"extensions":{"value":null,"problems":[{"path":[],"explanation":"Expected value to not be null"}]},"locations":[{"line":2,"column":69}],"message":"Variable $pullRequestId of type Int! was provided invalid value"}]

and

INFO: commenting on 2 GitHub issues:
  - 365
  - issuecomment-1478101323
ERROR: commenting on issue "Failed to create GitHub comment for "issuecomment-1478101323" issue." failed: undefined

You can see that the issue number of the referenced comment is incorrect—issuecomment-1478101323.