vim-patch:9.0.0604: luacheckrc file is not recognized (#20371)

Problem:    Luacheckrc file is not recognized.
Solution:   Use lua filetype for luacheckrc. (closes vim/vim#11236)
49c311c9b1

runtime/lua/vim/filetype.lua

@@ -1455,6 +1455,7 @@ local filename = {
   ['.sawfishrc'] = 'lisp',
   ['/etc/login.access'] = 'loginaccess',
   ['/etc/login.defs'] = 'logindefs',
+  ['.luacheckrc'] = 'lua',
   ['lynx.cfg'] = 'lynx',
   ['m3overrides'] = 'm3build',
   ['m3makefile'] = 'm3build',