disable compression on backup zips again

When backups were moved into a separate thread 5 years ago, it improved
performance when switching between different profiles, as the backup
happened in the background. But when closing Anki, we wait on the
background thread to complete, so Anki hangs until the backup finishes.

The performance difference on a large collection is considerable:

- 0.45s without compression
- 7.9s with compression

Given that the majority of users probably aren't using multiple profiles,
I think the speed increase is probably worth the extra disk usage. In
the future, we may want to look into using zstd to compress the backups,
which may even be a performance win over the uncompressed version on
some devices.

qt/aqt/main.py

@@ -650,7 +650,7 @@ class AnkiQt(QMainWindow):
                 pass
 
         def run(self) -> None:
-            z = zipfile.ZipFile(self.path, "w", zipfile.ZIP_DEFLATED)
+            z = zipfile.ZipFile(self.path, "w", zipfile.ZIP_STORED)
             z.writestr("collection.anki2", self.data)
             z.writestr("media", "{}")
             z.close()