Fix warning when using xcomarg dependencies (#26801)

This warning was invisible before 2.4 due to a bug in our logging config
(fixed by commit 7363e35) and AIP-45 which suddenly made this appear.

The problem was being caused by set_xcomargs_dependencies being called
once for each class in the hierarchy, and each of them doing the same
logic.

The fix is to look at the _actual_ function of `self.__init__` and
compare it to the function we're about to call so that we don't set
dependencies until we have finished the "outer" most class's
apply_defaults invocation.

(cherry picked from commit d77f056)

airflow/models/baseoperator.py

@@ -410,8 +410,9 @@ def apply_defaults(self: BaseOperator, *args: Any, **kwargs: Any) -> Any:
             # Store the args passed to init -- we need them to support task.map serialzation!
             self._BaseOperator__init_kwargs.update(kwargs)  # type: ignore
 
-            if not instantiated_from_mapped:
-                # Set upstream task defined by XComArgs passed to template fields of the operator.
+            # Set upstream task defined by XComArgs passed to template fields of the operator.
+            # BUT: only do this _ONCE_, not once for each class in the hierarchy
+            if not instantiated_from_mapped and func == self.__init__.__wrapped__:  # type: ignore[misc]
                 self.set_xcomargs_dependencies()
                 # Mark instance as instantiated.
                 self._BaseOperator__instantiated = True

tests/decorators/test_python.py

@@ -817,3 +817,18 @@ def down(a, b):
     assert len(decision.schedulable_tis) == 1  # "down"
     decision.schedulable_tis[0].run(session=session)
     assert result == "'example' None"
+
+
+@pytest.mark.filterwarnings("error")
+def test_no_warnings(reset_logging_config, caplog):
+    @task_decorator
+    def some_task():
+        return 1
+
+    @task_decorator
+    def other(x):
+        ...
+
+    with DAG(dag_id='test', start_date=DEFAULT_DATE, schedule=None):
+        other(some_task())
+    assert caplog.messages == []