This issue is now fixed on the oslo.messaging side [3], and in the way to be released [4]. Hence a new requirements update will arrive soon on the requirements side. This new version should fix the heat compatibility issue, thus, this will allow us to resync upper-constraints [5] and listed releases [6] before bobcat's final release.

[3] https://review.opendev.org/c/openstack/oslo.messaging/+/896422

[4] https://review.opendev.org/c/openstack/releases/+/896498

[6] https://releases.openstack.org/bobcat/index.html#bobcat-oslo-messaging

Thank you for considering this request.