Wait for preload creation independently of others

TaskGroup cancels the creation of other preloaded disposables in case
any fails to preload.

For: QubesOS/qubes-issues#10230
For: QubesOS/qubes-issues#1512

Author: ben-grande

qubes/vm/mix/dvmtemplate.py

@@ -493,11 +493,12 @@ async def on_domain_preload_dispvm_used(
                 return
 
         self.log.info("Preloading '%d' qube(s)", can_preload)
-        async with asyncio.TaskGroup() as task_group:
-            for _ in range(can_preload):
-                task_group.create_task(
-                    qubes.vm.dispvm.DispVM.from_appvm(self, preload=True)
-                )
+        await asyncio.gather(
+            *[
+                qubes.vm.dispvm.DispVM.from_appvm(self, preload=True)
+                for _ in range(can_preload)
+            ]
+        )
 
     def get_feat_preload_threshold(self) -> int:
         """