t_set.c comment update for srandmemberWithCountCommand (#7922)
t_set.c comment update for srandmemberWithCountCommand (#7922)

Reference the correct "case", case 4, in the comment explaining the need
for case 3, when the number of request items is too close to the
cardinality of the set. Case 4 is indeed the "natural approach"
referenced earlier in that sentence.
JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis