[cxx-interop] Fix predicate to find copy assignment operators.
[cxx-interop] Fix predicate to find copy assignment operators.

apple/swift,JGiola/swift,apple/swift,benlangmuir/swift,roambotics/swift,JGiola/swift,apple/swift,benlangmuir/swift,apple/swift,roambotics/swift,apple/swift,benlangmuir/swift,JGiola/swift,glessard/swift,JGiola/swift,glessard/swift,glessard/swift,glessard/swift,roambotics/swift,roambotics/swift,glessard/swift,glessard/swift,benlangmuir/swift,benlangmuir/swift,apple/swift,roambotics/swift,benlangmuir/swift,JGiola/swift,roambotics/swift,JGiola/swift