From Apple’s official unenroll beta page:

When your device is enrolled in the Apple Beta Software Program, you will automatically receive new versions of the public beta from the Mac App Store or iOS Software Update. At any time, you may unenroll your device so that it no longer receives these updates. You may also choose to leave the program entirely.

If you are enrolled in the beta program, you’ll get app store or software update updates for every beta that comes along. This is problematic if you don’t want to install an update. The beta notification will be stuck in your queue, like a piece of corn in your teeth.

Bookmark the page in case this every comes up for you.

[H/T the pugnaciously effervescent not Jony Ive]