test: correct osd pool default size

Using the default pool size of 2 with random eio thrashing can cause
some of the object to mark as lost.
fixing typo from 'osd default pool size: 3' to 'osd pool default size: 3'
so we will have pool size 3 correctly.

Fixes: https://tracker.ceph.com/issues/49888
Signed-off-by: Nitzan Mordechai <[email protected]>

Author: NitzanMordhai

qa/suites/rados/singleton/all/thrash-backfill-full.yaml

@@ -16,7 +16,7 @@ override:
   ceph:
     conf:
       mon:
-        osd default pool size: 3
+        osd pool default size: 3
         osd min pg log entries: 5
         osd max pg log entries: 10
 tasks:

qa/suites/rados/singleton/all/thrash-eio.yaml

@@ -12,11 +12,11 @@ openstack:
   - volumes: # attached to each instance
       count: 3
       size: 10 # GB
-override:
+overrides:
   ceph:
     conf:
       mon:
-        osd default pool size: 3
+        osd pool default size: 3
 tasks:
 - install:
 - ceph: