vim-patch:9.0.1229: Cap'n Proto files are not recognized (#21950)

Problem:    Cap'n Proto files are not recognized.
Solution:   Add a pattern and the "capnp" filetype. (Amaan Qureshi,
            closes vim/vim#11862)

040e795e8d

runtime/lua/vim/filetype.lua

@@ -190,6 +190,7 @@ local extension = {
   BUILD = 'bzl',
   qc = 'c',
   cabal = 'cabal',
+  capnp = 'capnp',
   cdl = 'cdl',
   toc = 'cdrtoc',
   cfc = 'cf',