And even if you read the banner on the site, the email they sent, and the announcement itself, you would not see instructions that mention the specific thing(s) you must change in order to opt out.
Sure, you can poke around in the settings and find one that you believe opts you out, but in lieu of clear and explicit instructions from GitHub, you'll have no way to find out. Only the possibility of finding out later that you guessed wrong.
So? You guarantee that this setting is durable and will never revert? Or you guarantee that no client-side bug on that page will not override the setting with null value when you click save on something else? Please.