Security isn’t absolute, it’s layered. The harder you make it for the adversary, the more it costs the adversary (eg: potentially burning a zero day), and the more chance there is of detection.
Can Russian intelligence get into Gitlab? Probably. Are measures that make it more expensive liable to deter them? I think so.
Two points here. First of all, failing to acheive absolute security is not a justification for ignoring best practices.
Second, this isn't air gapping. It is preventing a bugged laptop from sitting in on conference calls and meetings for the next year or two until it gets aged out.
Meanwhile, if the government can just arrest you and say "change this repository and you go free", it's essentially free.