Add "Learn Git Branching" (ja: interactive-tutorials) (#11154)

* add: Learn Git Branching

* fix: blank space between lines

more/free-programming-interactive-tutorials-ja.md

@@ -1,11 +1,17 @@
 ### Index
 
+* [Git](#git)
 * [HTML and CSS](#html-and-css)
 * [JavaScript](#javascript)
     * [React](#react)
 * [Python](#python)
 
 
+## Git
+
+* [Learn Git Branching](https://learngitbranching.js.org/?locale=ja)
+
+
 ### HTML and CSS
 
 * [レスポンシブウェブデザイン](https://www.freecodecamp.org/japanese/learn/responsive-web-design) - freeCodeCamp