test(lua): avoid async task completion flake #41702

Allow enough time for the timer and scheduled continuation to run on
Windows.

fixes #41699

AI-assisted

test/functional/lua/async_spec.lua

@@ -288,7 +288,7 @@ describe('async', function()
         return nil, 1
       end)
 
-      local r1, r2 = task:wait(10)
+      local r1, r2 = task:wait(100)
       eq(r1, nil)
       eq(r2, 1)
     end)