update: Pretend 4.0 exists

Created by: efritz

In order to unblock the product team issues in #40638, we need to be able to upgrade to a version at which the out of band migrations are deprecated (to exercise the full update code paths). We can't do that for real until we cut the 4.0 tag. Instead, we'll just choose some arbitrary head-of-main as the 4.0 release.

We can bump this hash freely up to the 4.0 release branch, at which point we should remove the function (but leave the new max version at 4.0).

Test plan

Tested locally.