test: Fix TestMachinesHostDevs race

Wait for the "Remove host device from VM?" dialog to disappear before
opening the "Add host device" dialog in the next test step. Otherwise it
often happend that the latter dialog just got opened, while
deleteResource.jsx' dialog shutdown handler called `Dialogs.close()`,
which would then close the new instead of the old dialog.

This is purely a test race, as a human user/browser won't allow
interaction with the main page as long as the modal dialog is still
open. But our CDP driver allows that.

Fixes #1292

test/check-machines-hostdevs

@@ -226,6 +226,7 @@ class TestMachinesHostDevs(VirtualMachinesCase):
                 b.wait_in_text("#delete-resource-modal-vendor", self._vendor)
 
                 b.click('.pf-v5-c-modal-box__footer button:contains("Remove")')
+                b.wait_not_present("#delete-resource-modal")
                 b.wait_not_present(f"#vm-subVmTest1-hostdev-{self.vm_dev_id}-product")
 
         # Check the error if selecting no devices when the VM is running