Simple enough: we should make it very clear in the Devguide that creating a PR from python:master to <username>:master is not a good way to update your fork.

For context, I recently saw that a commit on a fork was showing as a mention on a lot of the more recent commits to the master. I left a comment on the PR for the fork responsible to save them the embarrassment of this happening again (https://github.com/ThatXliner/cpython/pull/1#issuecomment-735969158 - my apologies to those who got pinged by that comment, I'm the one who feels embarrassed now!).

When I first started to contribute to CPython, I made exactly the same mistake (using a PR to update my fork - for the record I had never before used git except to clone). Yes, most of that was my ignorance but even after finding "Syncing with Upstream" (32.14 - which may make more sense renamed to "Updating your CPython fork" for accessibility but that's a separate issue), I did not think to combine it with the clone instructions of "Get the source code" (1.2 - I delete local copies when not in use to save space so only ran `git clone` before trying those on the guide).

That is also a separate issue and there is nothing we can do if people don't read the docs but IMO we should make it very clear that opening a PR on your fork is not a good solution to the problem (I don't want others making the same mistake, and it also unnecessarily pings quite a few of the core devs - though please correct me if I'm wrong and it doesn't ping them).