Show not supported exception for SyncCallback at Dag author time (apache#55390)

Currently, if a user uses SyncCallback for a DeadlineAlert without
reading docs, they will not find out that they're not currently
supported until the deadline is missed. So, this is just a
quality-of-life change to alert the user at Dag author time.

Author: ramitkataria

task-sdk/src/airflow/sdk/definitions/deadline.py

@@ -55,6 +55,9 @@ def __init__(
     ):
         self.reference = reference
         self.interval = interval
+
+        if not isinstance(callback, AsyncCallback):
+            raise ValueError(f"Callbacks of type {type(callback).__name__} are not currently supported")
         self.callback = callback
 
     def __eq__(self, other: object) -> bool:

task-sdk/tests/task_sdk/definitions/test_deadline.py

@@ -158,6 +158,14 @@ def test_deadline_alert_in_set(self):
         alert_set = {alert1, alert2}
         assert len(alert_set) == 1
 
+    def test_deadline_alert_unsupported_callback(self):
+        with pytest.raises(ValueError, match="Callbacks of type SyncCallback are not currently supported"):
+            DeadlineAlert(
+                reference=DeadlineReference.DAGRUN_QUEUED_AT,
+                interval=timedelta(hours=1),
+                callback=SyncCallback(TEST_CALLBACK_PATH),
+            )
+
 
 class TestCallback:
     @pytest.mark.parametrize(