They didn't, poor wording on Register part. The pull request was closed for inactivity by the bot.
We had technical problems that GitHub had no interest in solving, and lots of small frustrations with the platform built up over years.
Jumping from one enshittified profit-driven platform to another profit-driven platform would just mean we'd set ourselves up for another enshittification -> migration cycle later down the line.
No stunt here.
Btw why not GitLab?
If you try it, don't like it then don't use it, GitHub does not force you to use GHA anyway, and moving away from GitHub due to their direction sounds like a political movement. It's like someone who stop shopping from Walmart, not because they sells bad product but because they support the Republic, then going to a local shop that sometimes close unexpectedly sound unreasonable.