checker: fix missing error for non initialized interface struct member

vlib/v/checker/struct.v

@@ -672,8 +672,7 @@ fn (mut c Checker) struct_init(mut node ast.StructInit, is_field_zero_struct_ini
 				}
 				if !field.typ.has_flag(.option) && sym.kind == .interface_
 					&& (!has_noinit && sym.language != .js) && !node.has_update_expr {
-					// TODO: should be an error instead, but first `ui` needs updating.
-					c.note('interface field `${type_sym.name}.${field.name}` must be initialized',
+					c.error('interface field `${type_sym.name}.${field.name}` must be initialized',
 						node.pos)
 				}
 				// Do not allow empty uninitialized sum types

vlib/v/checker/tests/interface_init_err.out

@@ -1,4 +1,4 @@
-vlib/v/checker/tests/interface_init_err.vv:15:7: notice: interface field `Server.handler` must be initialized
+vlib/v/checker/tests/interface_init_err.vv:15:7: error: interface field `Server.handler` must be initialized
    13 | 
    14 | fn main() {
    15 |     _ := Server{}