GitHub integration doesn't work with non-master branches

[stamminator]

The following two URLs both use the master branch despite one of them specifying otherwise:

• ✅ https://jsfiddle.net/gh/get/library/pure/stamminator/jsfiddle-demos/tree/master/pleasant-toggle-button
• ❌ https://jsfiddle.net/gh/get/library/pure/stamminator/jsfiddle-demos/tree/main/pleasant-toggle-button

With GitHub now using main by default and there being no mention in the JSFiddle documentation about master branch being all that's supported, this has become quite a disruptive issue. I personally spent hours of trial and error figuring out how to get it to work, and judging by issues #1420 and #1665, which were closed but not fixed, others have too. Newcomers will likely see the state of things and assume it's broken, which I did as well before lots of digging.

Please revisit implementing a fix for this and updating the documentation.