Fix mypy error my creating a Task

Although Python doesn't support canceling coroutines in a different
thread, it allows gathering the result. QMemMan also doesn't allow
canceling API calls, so the cancel is a no-op.

Author: ben-grande

qubes/vm/dispvm.py

@@ -626,9 +626,11 @@ async def on_domain_pre_paused(self, event, **kwargs) -> None:
             return
         break_task = asyncio.create_task(self.preload_requested_event.wait())
         qmemman_client = qubes.qmemman.client.QMemmanClient()
-        qmemman_task = asyncio.to_thread(
-            qmemman_client.set_mem,
-            {self.xid: 0},
+        qmemman_task = asyncio.create_task(
+            asyncio.to_thread(
+                qmemman_client.set_mem,
+                {self.xid: 0},
+            )
         )
         tasks: list = [break_task, qmemman_task]
         result = None