Fix possible race condition when reading noMoreDrivers

The accessor noMoreDrivers is not synchronized (visibility is ensured by
the fact that noMoreDrivers is volatile). With current logic it was
possible to observe noMoreDrivers flag set to true while
DriverFactory.noMoreDrivers() was stil in progress and not all
OperatorFactory.noMoreOperators() methods completed.

core/trino-main/src/main/java/io/trino/operator/DriverFactory.java

@@ -140,10 +140,10 @@ public synchronized void noMoreDrivers()
         if (noMoreDrivers) {
             return;
         }
-        noMoreDrivers = true;
         for (OperatorFactory operatorFactory : operatorFactories) {
             operatorFactory.noMoreOperators();
         }
+        noMoreDrivers = true;
     }
 
     // no need to synchronize when just checking the boolean flag