Botulism spores are killed at a certain temperature for a certain amount of time, but I don't remember what those numbers are. Dunking a few garlic cloves in oil won't get you much garlic flavor anyway. Best is to crush the hell out of them and put the oil in the fridge. It will cloud a little, and take a little longer, but as long as you don't care about those things, it works well. Otherwise, you can simmer crushed garlic in oil. That will kill the botulism but the taste will be of cooked garlic.
Basically, botulism is anaerobic and lives in soil, so garlic, which is grown underground, and oil, which is oxygen free, is not a great mix.