Make buildQueryRunnerForSegment protected in ServerManager(#11493)

This is a minor change in ServerManager. Any sub-class can access the buildQueryRunnerForSegment in an extension if required.
diff --git a/server/src/main/java/org/apache/druid/server/coordination/ServerManager.java b/server/src/main/java/org/apache/druid/server/coordination/ServerManager.java
index 7f2b811..278f183 100644
--- a/server/src/main/java/org/apache/druid/server/coordination/ServerManager.java
+++ b/server/src/main/java/org/apache/druid/server/coordination/ServerManager.java
@@ -238,7 +238,7 @@
     );
   }
 
-  <T> QueryRunner<T> buildQueryRunnerForSegment(
+  protected <T> QueryRunner<T> buildQueryRunnerForSegment(
       final Query<T> query,
       final SegmentDescriptor descriptor,
       final QueryRunnerFactory<T, Query<T>> factory,