vim-patch:9.0.1430: Livebook files are not recognized (#22808)

Problem:    Livebook files are not recognized.
Solution:   Add a pattern for Livebook files. (Mathias Jean Johansen,
            closes vim/vim#12203)

6400203517

Co-authored-by: Mathias Jean Johansen <mathias@mjj.io>

runtime/lua/vim/filetype.lua

@@ -615,6 +615,7 @@ local extension = {
   asd = 'lisp',
   lt = 'lite',
   lite = 'lite',
+  livemd = 'livebook',
   lgt = 'logtalk',
   lotos = 'lotos',
   lot = 'lotos',