Version sync: restore verbose_name for stable version

[stsewd]

Closes #11939

This also discovered another problem, we are using the verbose name to check for latest/stable, but we should use the slug

readthedocs.org/readthedocs/vcs_support/backends/git.py

Lines 135 to 145 in 10d9ef9

	if self.version_machine and self.verbose_name == STABLE_VERBOSE_NAME:
	if self.version_identifier:
	return f"{self.version_identifier}"
	log.error("'stable' version without a commit hash.")
	return None
	tag_name = self.verbose_name
	# For a machine created "latest" tag, the name of the tag is set
	# in the `Version.identifier` field, note that it isn't a commit
	# hash, but the name of the tag.
	if self.version_machine and self.verbose_name == LATEST_VERBOSE_NAME:

Will try to fix that in another PR, as we need to pass the slug down...