Street Fighter 6 & Spy x Family Crossover Tag

BUR #59036 has been approved by @nonamethanks.

convert pool:21518 -> street_fighter_6_spy_x_family_collaboration

As suggested by forum #436584 to turn this into a tag rather than leaving it to crossover. Name suggestions greatly appreciated.

The bulk update request #59036 (forum #438046) has been approved by @nonamethanks.