time: add missing custom_format token (#18880)

vlib/time/custom_format_test.v

@@ -5,7 +5,7 @@ fn test_custom_format() {
 	assert date.custom_format('YYYY-MM-DD HH:mm') == date.format()
 	assert date.custom_format('MMM') == date.smonth()
 
-	test_str := 'M MM MMM MMMM\nD DD DDD DDDD\nd dd ddd dddd\nYY YYYY a A\nH HH h hh k kk e\nm mm s ss Z ZZ ZZZ\nDo DDDo Q Qo QQ\nN NN w wo ww\nM/D/YYYY N-HH:mm:ss Qo?a'
+	test_str := 'M MM Mo MMM MMMM\nD DD DDD DDDD\nd dd ddd dddd\nYY YYYY a A\nH HH h hh k kk e\nm mm s ss Z ZZ ZZZ\nDo DDDo Q Qo QQ\nN NN w wo ww\nM/D/YYYY N-HH:mm:ss Qo?a'
 
 	println(date.custom_format(test_str))
 }