vim-patch:9.2.0821: filetype: msmtp system-wide rc file not detected (#40895)

Problem:  filetype: msmtp system-wide rc file not detected (chdiza).
Solution: Detect 'msmtprc' as filetype msmtp, like '.msmtprc'
          (Doug Kearns).

fixes:  vim/vim#20751
closes: vim/vim#20752

https://github.com/vim/vim/commit/88440f9a3460bf54e4017340e764788dcf6cb3d7

Co-authored-by: Doug Kearns <dougkearns@gmail.com>

runtime/lua/vim/filetype.lua

@@ -1856,6 +1856,7 @@ local filename = {
   ['mplayer.conf'] = 'mplayerconf',
   mrxvtrc = 'mrxvtrc',
   ['.mrxvtrc'] = 'mrxvtrc',
+  msmtprc = 'msmtp',
   ['.msmtprc'] = 'msmtp',
   ['Muttngrc'] = 'muttrc',
   ['Muttrc'] = 'muttrc',