functests: Do not run termopen test on Windows

test/functional/core/main_spec.lua

@@ -59,6 +59,7 @@ describe('Command-line option', function()
       eq(#('100500\n'), attrs.size)
     end)
     it('does not crash after reading from stdin in non-headless mode', function()
+      if helpers.pending_win32(pending) then return end
       local screen = Screen.new(40, 8)
       screen:attach()
       funcs.termopen({