fix(utils): avoid vim.filetype.match in fast event (CopilotC-Nvim#1344)

Signed-off-by: Tomas Slusny <slusnucky@gmail.com>

Author: deathbeam

lua/CopilotChat/utils.lua

@@ -219,7 +219,7 @@ function M.filetype(filename)
     fs_access = false,
   })
 
-  if ft == '' or not ft then
+  if ft == '' or not ft and not vim.in_fast_event() then
     return vim.filetype.match({ filename = filename })
   end