I personally always call this a kittens-are-cute bill. The basic idea is that Party A wants to pass a certain bill, but they know it's wholly unacceptable to Party B. So what they do is add some (often only vaguely related) measure that will attract a lot of popular support from both parties' voters (as a joking example, "we hereby declare kittens to be cute"). Then they later point out that Party B voted against a bill that says kittens are cute (or that Party B abstained from voting, which to a lot of people is the same thing).
I see this strategy a lot, yet I don't remember ever seeing someone give a name to it. The word I'm looking for is not "omnibus bill", in that an omnibus bill can also be a true compromise where both parties get something they want. Not every omnibus bill is a kittens-are-cute bill, but of course every kittens-are-cute bill is, to some degree, an omnibus bill.
Note that whether or not Party A has a majority and as such gets the bill to pass is irrelevant. What's relevant is that all/most of Party B votes against, Party A knew this, and Party A decided to add a very popular measure to that same bill to later use as a rhetorical weapon.