False positive in pointless-reassignment when array on left hand side

[anderseknert]

Originally reported in #1277, but the two issues turned out to be unrelated, so I'm creating a separate issue for this.

This is currently reported as a pointless reassignment, but that should only apply when there is a single var on either side of the assignment:

parts := split(input.parts, ".")

s contains [b, a] if {
	[a, b] := parts
}