Update default sys-usb InputMouse policy for tests

In 4.1 mouse-action is configurable, which has an effect on the contents
of the policy.

See: https://github.com/QubesOS/qubes-mgmt-salt-dom0-virtual-machines/blob/78dcb14ef9b41650ec18ec0a40f44005ca1cafcc/pillar/qvm/sys-usb-allow-mouse.sls
and https://github.com/QubesOS/qubes-mgmt-salt-dom0-virtual-machines/blob/78dcb14ef9b41650ec18ec0a40f44005ca1cafcc/qvm/sys-usb.sls#L94

tests/vars/qubes-rpc-41.yml

@@ -33,7 +33,7 @@
 
 - policy: qubes.InputMouse
   starts_with: |-
-    sys-usb dom0 allow,user=root
+    sys-usb dom0 ask,user=root,default_target=dom0
     $anyvm $anyvm deny
 
 - policy: /etc/qubes-rpc/policy/qubes.PdfConvert