mon/OSDMonitor: do not populate void pg_temp into nextmap

Due to commit ea723fb, pg_temp with clean acting set are added to inc map.
The original intent was to clear out pg_temps during priming, but as
written it would set a new_pg_temp item clearing the pg_temp even if one
didn't already exist.  Adding the up != acting condition in there makes us
only take that path if there is an existing pg_temp entry to remove.

Fixes: https://tracker.ceph.com/issues/37784
Signed-off-by: Aleksei Zakharov <zakharov.a.g@yandex.ru>
(cherry picked from commit b1d3ca5)

src/mon/OSDMonitor.cc

@@ -1006,7 +1006,8 @@ void OSDMonitor::prime_pg_temp(
   int next_up_primary, next_acting_primary;
   next.pg_to_up_acting_osds(pgid, &next_up, &next_up_primary,
 			    &next_acting, &next_acting_primary);
-  if (acting == next_acting && next_up != next_acting)
+  if (acting == next_acting &&
+      !(up != acting && next_up == next_acting))
     return;  // no change since last epoch
 
   if (acting.empty())