test: Make test_bind_unbind_with_uclass() single-threaded

This test seems to rely on the other test in this file. Mark it
single-threaded to avoid any problems.

Signed-off-by: Simon Glass <sjg@chromium.org>

test/py/tests/test_bind.py

@@ -119,6 +119,7 @@ def get_next_line(tree, name):
 
 @pytest.mark.boardspec('sandbox')
 @pytest.mark.buildconfigspec('cmd_bind')
+@pytest.mark.singlethread
 def test_bind_unbind_with_uclass(u_boot_console):
     #bind /bind-test
     response = u_boot_console.run_command('bind  /bind-test simple_bus')