[CSL-1396] Add tests to 'instance Enum EpochOrSLot'
[CSL-1396] Add tests to 'instance Enum EpochOrSLot'

input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype