Removal of git:// protocol

[Aaron Meurer]

GitHub has removed support for the git:// protocol today. If you see a
message like

fatal: remote error:
The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/
for more information.

when trying to git pull SymPy, you will need to run

git remote set-url origin g...@github.com:sympy/sympy.git

(if you get the error for another remote than origin update the URL accordingly)

This is primarily of importance for people with push access, since the
guide at https://github.com/sympy/sympy/wiki/Pushing-patches used to
say to use git:// to avoid accidental pushing. Accidentally pushing to
the master branch is impossible due to branch protection, so you don't
need to worry about that. It is possible to accidentally push up
another branch to the main repo. If you do this, please delete it. All
pull requests branches should be made from forks (except for release
branches, which have to be on the main repo for technical reasons).

Another option for people with push access is to use something like
https://stackoverflow.com/questions/7556155/git-set-up-a-fetch-only-remote
to disable pushing to origin.

Aaron Meurer