Botulism spore growth is inhibited by acid, oxygen, alcohol, and competing microorganisms (amongst other factors). You have three of those four (and hopefully only three) in your beer, so you're good. There's no reason to worry.
To be a little more specific, pH levels below 4.6 and alcohol levels of 4-5% and above greatly reduce risk. Other factors support suppression of botulism spores and toxins. If you want more specific data, I'm sure I can find it. Just let me know. I don't think it's worth any of your time worrying about, though.