CI: lower ssPBCH_BlockPower in gNB conf for `RAN-SA-FHI72-CN5G` pipeline

Tests showed that a UE connected much faster, and did not fail as often
on Msg3.

ci-scripts/conf_files/gnb.sa.band77.273prb.fhi72.4x4-vvdn.conf

@@ -152,7 +152,7 @@ gNBs =
       nrofUplinkSlots                                               = 1;
       nrofUplinkSymbols                                             = 4;
 
-  ssPBCH_BlockPower                                                 = 0;
+  ssPBCH_BlockPower                                                 = -10;
   }
 
   );