vim-patch:9.1.0307: filetype: texdoc config files is not recognized

Problem:  filetype: texdoc config files is not recognized
Solution: Detect 'texdoc.cnf' as conf filetype
          (Wu, Zhenyu)

See: https://github.com/TeX-Live/texdoc/blob/master/texdoc.cnf

closes: vim/vim#14507

7fdbd1bb58

Co-authored-by: Wu, Zhenyu <wuzhenyu@ustc.edu>

runtime/lua/vim/filetype.lua

@@ -1302,6 +1302,7 @@ local filename = {
   ['csh.login'] = detect.csh,
   ['csh.logout'] = detect.csh,
   ['auto.master'] = 'conf',
+  ['texdoc.cnf'] = 'conf',
   ['.x11vncrc'] = 'conf',
   ['configure.in'] = 'config',
   ['configure.ac'] = 'config',