test: restore timeout after bootmenu unit test

In the bootmenu unit test the console timeout is set to 500 ms.
Other tests rely on the original timeout. Ensure that the original value
is restored.
Signed-off-by: NHeinrich Schuchardt <heinrich.schuchardt@canonical.com>

test/py/tests/test_bootmenu.py

@@ -11,7 +11,7 @@ def test_bootmenu(u_boot_console):
     u_boot_console -- U-Boot console
     """
 
-    u_boot_console.p.timeout = 500
+    with u_boot_console.temporary_timeout(500):
         u_boot_console.run_command('setenv bootmenu_default 1')
         u_boot_console.run_command('setenv bootmenu_0 test 1=echo ok 1')
         u_boot_console.run_command('setenv bootmenu_1 test 2=echo ok 2')