vim-patch:9.1.0880: filetype: C3 files are not recognized

Problem:  filetype: C3 files are not recognized
Solution: detect '*.c3*' files as c3 filetype (Turiiya)

closes: vim/vim#16087

c8dfcfc53b

Co-authored-by: Turiiya <34311583+ttytm@users.noreply.github.com>

runtime/lua/vim/filetype.lua

@@ -275,6 +275,9 @@ local extension = {
   mdh = 'c',
   epro = 'c',
   qc = 'c',
+  c3 = 'c3',
+  c3i = 'c3',
+  c3t = 'c3',
   cabal = 'cabal',
   cairo = 'cairo',
   capnp = 'capnp',