Modify error message wording

Signed-off-by: Chen Dai <[email protected]>

flint-spark-integration/src/main/scala/org/opensearch/flint/spark/mv/FlintSparkMaterializedView.scala

@@ -135,7 +135,7 @@ case class FlintSparkMaterializedView(
           Some(agg, attr)
         case _ =>
           throw new IllegalArgumentException(
-            s"Tumble function only supports time column, but found: $timeCol")
+            s"Tumble function only supports simple timestamp column, but found: $timeCol")
       }
     }
 

integ-test/src/integration/scala/org/opensearch/flint/spark/FlintSparkMaterializedViewSqlITSuite.scala

@@ -472,7 +472,7 @@ class FlintSparkMaterializedViewSqlITSuite extends FlintSparkSuite {
                |""".stripMargin)
         }
         ex.getCause should have message
-          "Tumble function only supports time column, but found: cast('timestamp as timestamp)"
+          "Tumble function only supports simple timestamp column, but found: cast('timestamp as timestamp)"
       }
     }
   }