vim-patch:9.1.2061: filetype: Koka files are not recognized

Problem:  filetype: Koka files are not recognized
Solution: Detect *.kk files as koka filetype (Hoang Nguyen).

Reference:
- https://koka-lang.github.io/koka/doc/index.html

closes: vim/vim#19104

969a4a0ba5

Co-authored-by: Hoang Nguyen <folliekazetani@protonmail.com>

runtime/lua/vim/filetype.lua

@@ -691,6 +691,7 @@ local extension = {
   kerml = 'kerml',
   kv = 'kivy',
   kix = 'kix',
+  kk = 'koka',
   kos = 'kos',
   kts = 'kotlin',
   kt = 'kotlin',