haskell-syb-0.4.1: disable the test suite when compiling with GHC HEAD

The test suite fails in a seemingly harmless way:

  ### Failure in: All:0
  expected: "(MyDataType Int,(DataType {tycon = \"MyDataType\", datarep = AlgRep [MyDataType]},(\"\",(\"MyDataType\",(\"\",\"MyDataType\")))))"
   but got: "(MyDataType Int,(DataType {tycon = \"Datatype.MyDataType\", datarep = AlgRep [MyDataType]},(\"\",(\"MyDataType\",(\"Datatype\",\"MyDataType\")))))"