Fix optimized plan string in EsqlSession (elastic#136689)

Thanks for the catch @idegtiarenko !

Author: alex-spies

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/session/EsqlSession.java

@@ -924,11 +924,12 @@ public void preOptimizedPlan(
     }
 
     private PhysicalPlan physicalPlan(Versioned<LogicalPlan> optimizedPlan) {
-        if (optimizedPlan.inner().optimized() == false) {
+        LogicalPlan logicalPlan = optimizedPlan.inner();
+        if (logicalPlan.optimized() == false) {
             throw new IllegalStateException("Expected optimized plan");
         }
-        optimizedLogicalPlanString = optimizedPlan.toString();
-        var plan = mapper.map(optimizedPlan);
+        optimizedLogicalPlanString = logicalPlan.toString();
+        PhysicalPlan plan = mapper.map(optimizedPlan);
         LOGGER.debug("Physical plan:\n{}", plan);
         return plan;
     }