Build failure on GHC 9.6

[locallycompact]

Looks like an API change on 9.6

doctest> [ 1 of 16] Compiling GhcUtil          ( src/GhcUtil.hs, dist/build/GhcUtil.o, dist/build/GhcUtil.dyn_o )
doctest> src/GhcUtil.hs:73:19: error: [GHC-88464]
doctest>     Data constructor not in scope: NoBackend :: Backend
doctest>     Suggested fix: Perhaps use variable ‘noBackend’ (imported from GHC)
doctest>    |
doctest> 73 |       backend   = NoBackend
doctest>    |                   ^^^^^^^^^
doctest> [ 2 of 16] Compiling Language.Haskell.GhciWrapper ( ghci-wrapper/src/Language/Haskell/GhciWrapper.hs, dist/build/Language/Haskell/GhciWrapper.o, dist/build/Language/Haskell/GhciWrapper.dyn_o )
doctest> [ 3 of 16] Compiling Interpreter      ( src/Interpreter.hs, dist/build/Interpreter.o, dist/build/Interpreter.dyn_o )
doctest> [ 4 of 16] Compiling Location         ( src/Location.hs, dist/build/Location.o, dist/build/Location.dyn_o )
doctest> [ 5 of 16] Compiling PackageDBs       ( src/PackageDBs.hs, dist/build/PackageDBs.o, dist/build/PackageDBs.dyn_o )
doctest> [ 6 of 16] Compiling Paths_doctest    ( dist/build/autogen/Paths_doctest.hs, dist/build/Paths_doctest.o, dist/build/Paths_doctest.dyn_o )
doctest> [ 7 of 16] Compiling Info             ( src/Info.hs, dist/build/Info.o, dist/build/Info.dyn_o )
doctest> [ 8 of 16] Compiling Options          ( src/Options.hs, dist/build/Options.o, dist/build/Options.dyn_o )
doctest> [ 9 of 16] Compiling Util             ( src/Util.hs, dist/build/Util.o, dist/build/Util.dyn_o )
error: builder for '/nix/store/7mn69kvw5wn7f1nr43qmal2f8n1akys4-doctest-0.20.1.drv' failed with exit code 1;

https://gitlab.homotopic.tech/horizon/horizon-core/-/jobs/161052

[sol]

This will be fixed by #401.