My impression (NOT A LAWYER) is that by hosting your code in a public repo on GitHub, you agree to their terms and give them the right to "read" your code including training AI models on it. Or at least that's what they're banking on.
Go host on Sourcehut or self-host with Gitea, and I would think it unlikely (but not impossible) that any big company would use your code to train their AI.
Just imagine, there's really nothing preventing people from scraping your blog to train their natural language processing AI or whatever, why would code be any different? Even if you put up a big sign saying you don't consent to having your data ingested by a neural network, I doubt it will get noticed anyway...
People have been taking large OSS codebases (eg. Linux kernel) for various statistical analyses. AI is just doing the same thing in a more sophisticated manner.
https://twitter.com/NoraDotCodes/status/1412741339771461635
There's also other references that GitHub public repos weren't the only source. They trawl other publicly readable code.
