T12087.hs:6:20: error: [GHC-71492]
    GADT constructor type signature cannot contain nested ‘forall’s or contexts
    In the definition of data constructor ‘MkF1’

T12087.hs:9:25: error: [GHC-71492]
    GADT constructor type signature cannot contain nested ‘forall’s or contexts
    In the definition of data constructor ‘MkF2’

T12087.hs:12:34: error: [GHC-71492]
    GADT constructor type signature cannot contain nested ‘forall’s or contexts
    In the definition of data constructor ‘MkF3’

T12087.hs:15:36: error: [GHC-71492]
    GADT constructor type signature cannot contain nested ‘forall’s or contexts
    In the definition of data constructor ‘MkF4’

T12087.hs:18:25: error: [GHC-71492]
    GADT constructor type signature cannot contain nested ‘forall’s or contexts
    In the definition of data constructor ‘MkF5’