doc: fix release guide example consistency
This changeset fixes two consistency issues in this single example that guides releasers on how to push the tag to the remote repo.
The first issue is that the remote git reference is consistently
referred to as upstream
elsewhere in the guide.
The second issue being that the version example used in the rest of the
guide should be a fictional v1.2.3
as stated in the How to create a
release section notes:
- Examples will use the fictional release version
1.2.3
.
cc @nodejs/releasers