They did not disallow LLM contributions, and they definitely didn't disallow using LLMs to research security vulnerabilities. They only disallowed projects that are majority LLM-written.
https://codeberg.org/Codeberg/org/commit/71149c7fc95ccfeae36...
That is about Codeberg, not Forgejo.
Forgejo disallows LLM contributions, including using a "general AI" (they include LLMs under "general AI") for reviews[0]:
> 5. Using general AI for review is forbidden. If the change contains changes to the UX it has to be approved by a human reviewer.
[0] https://codeberg.org/forgejo/governance/src/branch/main/AIAg...