fix(utils): `do_or_fail` `res` need to be promoted

src/awesomewm.d.tl/utils.tl

@@ -58,12 +58,12 @@ function utils.do_or_fail<T>(func: function<T>(...: any): (T | nil, string), ...
 
    local ok, res, err = pcall(func, ...)
 
-   if not (ok and res) then
+   if not ok then
       log:error(logger.message_with_metadata("do_or_fail failed!", { error = err }))
       error(err)
    end
 
-   return res
+   return res as T -- promote to T since pcall succeeded at this point
 end
 
 return utils