vim-patch:9.1.2110: filetype: skhd files are not recognized

Problem:  filetype: skhd files are not recognized
Solution: Detect .skhdrc and skhdrc as skhd filetype,
          include a syntax and filetype plugin, add syntax tests
          (Kiyoon Kim)

Add syntax highlighting for skhd (simple hotkey daemon for macOS)
configuration files. Includes filetype detection for skhdrc and
.skhdrc files.

Reference:
- https://github.com/asmvik/skhd

closes: vim/vim#19235

e5f61842b5

Co-authored-by: Kiyoon Kim <kiyoon@users.noreply.github.com>

runtime/lua/vim/filetype.lua

@@ -1906,6 +1906,8 @@ local filename = {
   ['.tcshrc'] = detect.tcsh,
   ['tcsh.login'] = detect.tcsh,
   ['tcsh.tcshrc'] = detect.tcsh,
+  ['.skhdrc'] = 'skhd',
+  ['skhdrc'] = 'skhd',
   ['/etc/slp.conf'] = 'slpconf',
   ['/etc/slp.reg'] = 'slpreg',
   ['/etc/slp.spi'] = 'slpspi',