Using enums in a card/deck class
Your implementation uses Enum for the suits, but not for the values.  Thus it is harder to validate the card values, and would as you noted, allow a joker card to be created, even though you didn't want that ability. 

Card Value Enum:

A card value enum provides the ability to give the cards a value and a descriptive name, while limiting possible values to valid ranges:

class CardValue(Enum):
    Ace = 1
    Deuce = 2
    Three = 3
    Four = 4
    Five = 5
    Six = 6
    Seven = 7
    Eight = 8
    Nine = 9
    Ten = 10
    Jack = 11
    Queen = 12
    King = 13


Immutable Types

For something like a card, an immutable type can provide some advantages.  One big one, is that the same value and suit will always key the same in a set or dict. Inheriting from tuple will achieve imuutability.  Note that the class is setup in __new__ not __init__ since it is immutable.

class Card(tuple):

    def __new__(cls, value, suit):
        assert isinstance(value, CardValue)
        assert isinstance(suit, CardSuit)
        return tuple.__new__(cls, (value, suit))


property decorator

The property decorator makes it easy to access the value and suit.

    @property
    def value(self):
        return self[0]

    @property
    def suit(self):
        return self[1]


__str__ method

Since we are using Enum's for all of the values, a fully descriptive __str__ method is quite straight forward:

    def __str__(self):
        return "{} of {}s".format(self.value.name, self.suit.name)


So something like:

print(Card(CardValue.Ace, CardSuit.Club))


gives:

Ace of Clubs


Make sure we stay immutable

Suggest adding some boilerplate to help avoid abusing the class instances.

    def __setattr__(self, *ignored):
        raise NotImplementedError

    def __delattr__(self, *ignored):
        raise NotImplementedError


Deck class

So the Deck class can be made much simpler with the new Value class and a set comprehension like:

class Deck:
    def __init__(self):
        self.cards = {
            Card(value, suit) for value in CardValue for suit in CardSuit
        }


Whole Listing:

from enum import Enum

class CardValue(Enum):
    Ace = 1
    Deuce = 2
    Three = 3
    Four = 4
    Five = 5
    Six = 6
    Seven = 7
    Eight = 8
    Nine = 9
    Ten = 10
    Jack = 11
    Queen = 12
    King = 13


class CardSuit(Enum):
    Club = 1
    Heart = 2
    Diamond = 3
    Spade = 4


class Card(tuple):

    def __new__(cls, value, suit):
        assert isinstance(value, CardValue)
        assert isinstance(suit, CardSuit)
        return tuple.__new__(cls, (value, suit))

    @property
    def value(self):
        return self[0]

    @property
    def suit(self):
        return self[1]

    def __str__(self):
        return "{} of {}s".format(self.value.name, self.suit.name)

    def __setattr__(self, *ignored):
        raise NotImplementedError

    def __delattr__(self, *ignored):
        raise NotImplementedError

class Deck:
    def __init__(self):
        self.cards = {
            Card(value, suit) for value in CardValue for suit in CardSuit
        }