Add a link to "Learn Git Branching" tutorial to "Branching Basics" topic in "Git & Github" roadmap & rename file in "Backend" roadmap content. (#7250)

Added "Learn Git Branching" tutorial link.

src/data/roadmaps/git-github/content/branching-basics@bXfCUG3h1TIFPgD4WUDph.md

@@ -5,4 +5,5 @@ Branches in Git serve as separate lines of development that allow multiple featu
 Visit the following resources to learn more:
 
 - [@official@Git Branching - Basic Branching and Merging](https://git-scm.com/book/en/v2/Git-Branching-Basic-Branching-and-Merging)
-- [@video@Git Branches Tutorial](https://www.youtube.com/watch?v=e2IbNHi4uCI)
+- [@article@Learn Git Branching](https://learngitbranching.js.org/)
+- [@video@Git Branches Tutorial](https://www.youtube.com/watch?v=e2IbNHi4uCI)