markused: fix mark for array init from sumtype (fix #24887) (#24889)

vlib/v/checker/struct.v

@@ -865,6 +865,8 @@ or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.',
 				mut info := first_sym.info as ast.Struct
 				c.check_uninitialized_struct_fields_and_embeds(node, first_sym, mut info, mut
 					inited_fields)
+			} else if first_sym.kind == .array {
+				c.table.used_features.arr_init = true
 			}
 		}
 		.none {

vlib/v/tests/skip_unused/array_init_from_sumtype.vv

@@ -0,0 +1,5 @@
+type Dict = []string | string
+
+fn main() {
+	_ := Dict{}
+}