stage_release runs on every push to main and unconditionally deletes
and recreates the draft release for the version in _version.py. Since
_version.py isn't bumped until sometime after a release is tagged and
published by release.yml, every intervening push to main was clobbering
the just-published release back to draft status. Confirmed this hit
v17.3.0 through v17.8.0 (and briefly v17.8.1, manually fixed).
Skip the delete/recreate if a non-draft release already exists for
this tag.
James R. Barlow
f0a3a74374