Java SDK: Write each Dag tag once, as Python does

Author: jason810496

java-sdk/sdk/src/main/kotlin/org/apache/airflow/sdk/execution/Serde.kt

@@ -167,7 +167,7 @@ private fun applyDagConfig(
   (config["tags"] as? List<*>)?.let { tags ->
     // Python stores tags in a set and serializes them sorted (for a stable
     // dag_hash); mirror that regardless of registration order.
-    data["tags"] = tags.map { it.toString() }.sorted()
+    data["tags"] = tags.map { it.toString() }.distinct().sorted()
   }
   listOf(
     "max_active_tasks",

java-sdk/sdk/src/test/kotlin/org/apache/airflow/sdk/execution/SerdeTest.kt

@@ -119,7 +119,7 @@ internal class SerdeTest {
     val dag =
       DagDef("d")
         .config("description", "demo")
-        .config("tags", listOf("b", "a"))
+        .config("tags", listOf("b", "a", "b"))
         .config("catchup", true)
         .config("fail_fast", true)
         .config("max_active_runs", 3)