T14720 fails with Core Lint failure in DEBUG compiler

Found while looking at !2890:

Compile failed (exit code 1) errors were:                                                                                              
*** Core Lint errors : in result of Worker Wrapper binds ***                                                                                                                                                                                                                  
T14270.hs:86:1: warning:                                                                                                               
    Non-top-level binder has an external name: typeRepKind                                                                             
    In the RHS of typeRepKind :: forall k (a :: k).                                                                                                                                                                                                                           
                                 TypeRep a -> TypeRep k                                                                                                                                                                                                                       
    Substitution: [TCvSubst                                                                                                                                                                                                                                                   
                     In scope: InScope {}                                                                                              
                     Type env: []                                                                                                      
                     Co env: []]