Nothing is stopping this person from sending email patches like they do in the Linux kernel project. No sanctions are involved in this person hosting a Git installation in Crimea that the rest of the world can access.
The problem isn't politics. The problem is that programmer culture currently conflates "access to Github" (which is a service run at the whims of an American defense contractor) with "free or open-source software" (which is a spectrum of opinions about copyright law). They are not related concepts, no matter what Github's marketing team has convinced the world.
I therefore agree with the view that 'free software' is a social movement, while 'open source' is a development methodology.
OSS is full of commercial interests well beyond hobby interests. Joel Spolsky pointed that out in https://www.joelonsoftware.com/2002/06/12/strategy-letter-v/ :
> I noticed something interesting about open source software, which is this: most of the companies spending big money to develop open source software are doing it because it’s a good business strategy for them, not because they suddenly stopped believing in capitalism and fell in love with freedom-as-in-speech.
The free software movement is itself political - as are all social movements. For example, the emphasis on end-user freedoms related to copyright protection conflict with the emphasis on worker rights embodied in the Anti 996 License.
This isn't a free speech issue. It's not even a corporate free speech issue. This is commercial activity.
Whether this is good policy or not, is another matter but it isn't a free speech matter.
Seeing free/open source software in the same light ideologically is not that much of a leap. There is precedent.
GitHub is a subsidiary of Microsoft, a US company with lucrative interests in the US government. While this does indeed stifle OSS activity for people in Crimea it isn't really about OSS.
These sanctions tend not to be universal and some services can continue to be provided, however the price of violating said sanctions can be very severe.
I don’t know how many people who work at Github or PayPal especially senior management are willing to risk fines not to mention jail time for something as simple as some Russian officer buying a DVD on the internet while being stationed in Crimea or a local IT guy from the current pro-Russian government making a pull request.
Then don't use github. I don't. It's completely toxic.