Cancel the deprecation of GitHub and other custom git sources

[deivid-rodriguez]

We were planning to deprecate :github and other custom git sources in favor of "do it in your own Gemfile" solutions. However, I think GitHub is so common that it's really handy that bundler provides it by default. A while ago I postponed the deprecation to after bundler 3, because I thought it would create too much friction with users for bundler 3. But now I find myself accepting new features for it, and had even forgotten we still plan to deprecate it later.

My proposal is to stick to the custom git sources that we currently have. They're not too hard to maintain and they are very useful for the community. If we get a new feature proposal in the future for some new uncommon source control website, we may want to reject that but I think it's wise to keep what we have now.

[hsbt]

I agreed your proposal. There is no strong reason to remove it.

[deivid-rodriguez]

I proposed a PR: #5147.

[duckinator]

This was resolved by #5147 in December 2021.