Ok, I see. First, the option that turns this warning on or off is under Tools > Global Options as shown here (and indeed described a bit different from the actual warning):

Second, to get the mtcars example to exhibit this behavior, you need to remove the rename line:
df <- mtcars %>%
select(dataset)
Of course this means that dataset would now not actually be in your data.frame, but that does trigger the warning you describe. There may be something going wrong with the bit of code in lines ~31-33 in your original example?