Surprising specialisation with INCOHERENT and rank 2 types

Summary

See README: https://gitlab.haskell.org/Leary/repro-ivts

Steps to reproduce

Run cabal test or ./ghc-test -O1 in the linked repo.

Expected behavior

The test should pass.

Environment

• GHC version used: 9.8.2; 9.10.1

Optional:

• Operating System: NixOS
• System Architecture: x86_64