vim-patch:9.1.1299: filetype: mbsyncrc files are not recognized

Problem:  filetype: mbsyncrc files are not recognized
Solution: detect isyncrc and "*.mbsyncrc" files as mbsync filetype,
          include filetype and syntax plugin (Pierrick Guillaume)

mbsync is a command line application which synchronizes mailboxes;
currently Maildir and IMAP4 mailboxes are supported.
New messages, message deletions and flag changes can be propagated both ways;
the operation set can be selected in a fine-grained manner.

References:
mbsync syntax overview: mbsync manual (isync v1.4.4)
https://isync.sourceforge.io/mbsync.html

Upstream support for the mbsync filetype.
Original plugin: https://github.com/Fymyte/mbsync.vim

closes: vim/vim#17103

836b87d699

Co-authored-by: Pierrick Guillaume <pguillaume@fymyte.com>

runtime/lua/vim/filetype.lua

@@ -762,6 +762,7 @@ local extension = {
   dm3 = 'maxima',
   dmt = 'maxima',
   wxm = 'maxima',
+  mbsyncrc = 'mbsync',
   mw = 'mediawiki',
   wiki = 'mediawiki',
   mel = 'mel',
@@ -1502,7 +1503,6 @@ local filename = {
   ['.chktexrc'] = 'conf',
   ['.ripgreprc'] = 'conf',
   ripgreprc = 'conf',
-  ['.mbsyncrc'] = 'conf',
   ['configure.in'] = 'config',
   ['configure.ac'] = 'config',
   crontab = 'crontab',
@@ -1705,6 +1705,7 @@ local filename = {
   ['/etc/man.conf'] = 'manconf',
   ['man.config'] = 'manconf',
   ['maxima-init.mac'] = 'maxima',
+  isyncrc = 'mbsync',
   ['meson.build'] = 'meson',
   ['meson.options'] = 'meson',
   ['meson_options.txt'] = 'meson',