fix: properly highlight multi filetype code blocks (#1926)

lua/avante/utils/init.lua

@@ -1083,7 +1083,8 @@ function M.get_filetype(filepath)
   local buf = vim.api.nvim_create_buf(false, true)
   local filetype = vim.filetype.match({ filename = filepath, buf = buf }) or ""
   vim.api.nvim_buf_delete(buf, { force = true })
-
+  -- Parse the first filetype from a multifiltype file
+  filetype = filetype:gsub("%..*$", "")
   return filetype
 end