colbuilder: address a minor nit in a recent fix

In 7ad29c3 we made some changes about
how argument to window functions are being cast to the same type in some
cases. After the cast we now update the column index but forgot to
update the type to the new one. However, this doesn't lead to problems
since `argTypes` is only used by the aggregate window functions, and the
casts can only be needed for non-aggregate window functions. Still, it's
better to update the types to avoid confusion.

Release note: None

pkg/sql/colexec/colbuilder/execplan.go

@@ -1237,6 +1237,7 @@ func NewColOperator(
 					}
 					typs = append(typs, typ)
 					argIdxs[i] = castIdx
+					argTypes[i] = typ
 				}
 
 				partitionColIdx := tree.NoColumnIdx