fix code conflict

Author: seawinde

fe/fe-core/src/main/java/org/apache/doris/nereids/rules/exploration/mv/InitMaterializationContextHook.java

@@ -36,6 +36,7 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
+import java.util.ArrayList;
 import java.util.BitSet;
 import java.util.List;
 import java.util.Set;