Fix flaky K8s xcom tests on ARM runners hitting 120s pod-start timeout (#65598)

On ARM CI runners with a cold containerd cache, the first test in the K8s
system suite that needs the xcom sidecar image (alpine) or the basic_pod
template's image can exceed KubernetesPodOperator's 120s startup budget,
producing a PodLaunchTimeoutException that surfaces as a generic
"AirflowException: Pod ... returned a failure".

Two changes:

- basic_pod.yaml / test_full_pod_spec now use `ubuntu` instead of `perl`.
  The pod only runs `/bin/bash -c 'echo ... > /airflow/xcom/return.json'`,
  so any image with bash works, and `ubuntu` is already warmed by earlier
  tests in the same suite — no extra image pull needed.

- Every real-cluster test that sets `do_xcom_push=True` now passes
  `startup_timeout_seconds=XCOM_STARTUP_TIMEOUT_SECONDS` (300s). Since
  pytest ordering is not guaranteed, whichever xcom test runs first has to
  absorb the one-time alpine sidecar pull; bumping the budget on all of
  them keeps the suite order-independent.

Observed failure: apache/airflow actions run 24716106401, job 72301089157
(K8S System:CeleryExecutor-3.12-v1.32.8-false, ARM). Both failing tests
took exactly ~120s matching the default startup_timeout_seconds; pod
events showed "Pulling image 'alpine' ..." with no "Successfully pulled"
inside the 120s window.

No production code change — the operator default of 120s is unchanged.

Author: potiuk

kubernetes-tests/tests/kubernetes_tests/basic_pod.yaml

@@ -23,7 +23,7 @@ metadata:
 spec:
   containers:
     - name: base
-      image: perl
+      image: ubuntu
       command: ["/bin/bash"]
       args: ["-c", 'echo {\"hello\" : \"world\"} | cat > /airflow/xcom/return.json']
   restartPolicy: Never

kubernetes-tests/tests/kubernetes_tests/test_kubernetes_pod_operator.py

@@ -51,6 +51,12 @@
 HOOK_CLASS = "airflow.providers.cncf.kubernetes.operators.pod.KubernetesHook"
 POD_MANAGER_CLASS = "airflow.providers.cncf.kubernetes.utils.pod_manager.PodManager"
 
+# Longer than the operator's 120s default to absorb the first-pull latency of
+# the xcom sidecar image (alpine) on ARM runners with a cold containerd cache.
+# Whichever xcom test runs first has to pay that cost; giving all of them the
+# same budget keeps the tests order-independent.
+XCOM_STARTUP_TIMEOUT_SECONDS = 300
+
 
 def create_context(task) -> Context:
     from tests_common.test_utils.version_compat import AIRFLOW_V_3_0_PLUS
@@ -709,6 +715,7 @@ def test_xcom_push(self, test_label):
             task_id=str(uuid4()),
             in_cluster=False,
             do_xcom_push=True,
+            startup_timeout_seconds=XCOM_STARTUP_TIMEOUT_SECONDS,
         )
         context = create_context(k)
         assert k.execute(context) == expected
@@ -753,6 +760,7 @@ def test_pod_template_file_system(self, basic_pod_template):
             labels=self.labels,
             pod_template_file=basic_pod_template.as_posix(),
             do_xcom_push=True,
+            startup_timeout_seconds=XCOM_STARTUP_TIMEOUT_SECONDS,
         )
 
         context = create_context(k)
@@ -775,6 +783,7 @@ def test_pod_template_file_with_overrides_system(self, env_vars, test_label, bas
             in_cluster=False,
             pod_template_file=basic_pod_template.as_posix(),
             do_xcom_push=True,
+            startup_timeout_seconds=XCOM_STARTUP_TIMEOUT_SECONDS,
         )
 
         context = create_context(k)
@@ -814,6 +823,7 @@ def test_pod_template_file_with_full_pod_spec(self, test_label, basic_pod_templa
             pod_template_file=basic_pod_template.as_posix(),
             full_pod_spec=pod_spec,
             do_xcom_push=True,
+            startup_timeout_seconds=XCOM_STARTUP_TIMEOUT_SECONDS,
         )
 
         context = create_context(k)
@@ -842,7 +852,7 @@ def test_full_pod_spec(self, test_label):
                 containers=[
                     k8s.V1Container(
                         name="base",
-                        image="perl",
+                        image="ubuntu",
                         command=["/bin/bash"],
                         args=["-c", 'echo {\\"hello\\" : \\"world\\"} | cat > /airflow/xcom/return.json'],
                         env=[k8s.V1EnvVar(name="env_name", value="value")],
@@ -858,7 +868,7 @@ def test_full_pod_spec(self, test_label):
             full_pod_spec=pod_spec,
             do_xcom_push=True,
             on_finish_action=OnFinishAction.KEEP_POD,
-            startup_timeout_seconds=30,
+            startup_timeout_seconds=XCOM_STARTUP_TIMEOUT_SECONDS,
         )
 
         context = create_context(k)