Improve auto-deprecation process
The current auto-deprecation process causes API breakages when we branch for the next release, e.g. the start of the 2025.1 release cycle.
When we upgrade `BACK_COMPAT_TO` add-ons begin to receive API breakage warnings. Generally we want to update `BACK_COMPAT_TO` before any API breaking changes.
Sometimes we may start the 20XX.1 release cycle, updating `version_year` before we update `BACK_COMPAT_TO`.
This causes API deprecations to break before add-ons are declared as incompatible.
Description of user facing changes
None
Description of development approach
minor fix up to existing deprecation pending removal
