[AIRFLOW-XXXX] Fix typo in example_bigquery DAG

[ryanyuan]

Fix typo in example_bigquery DAG. Task id in xcom_pull should match the real task id, which is "get_data".

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Issue link: Document only change, no JIRA issue

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[ryanyuan]

@mik-laj PTAL

[codecov-io]

Codecov Report

Merging #7429 into master will increase coverage by 52.87%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #7429       +/-   ##
===========================================
+ Coverage   32.91%   85.79%   +52.87%     
===========================================
  Files         877      878        +1     
  Lines       41150    41505      +355     
===========================================
+ Hits        13545    35608    +22063     
+ Misses      27605     5897    -21708

Impacted Files	Coverage Δ
...ders/google/cloud/example_dags/example_bigquery.py	100% <ø> (ø)	⬆️
airflow/kubernetes/volume_mount.py	44.44% <0%> (-55.56%)	⬇️
airflow/kubernetes/volume.py	52.94% <0%> (-47.06%)	⬇️
airflow/kubernetes/pod_launcher.py	47.18% <0%> (-39.44%)	⬇️
...viders/cncf/kubernetes/operators/kubernetes_pod.py	69.38% <0%> (-25.52%)	⬇️
airflow/kubernetes/refresh_config.py	50.98% <0%> (-23.53%)	⬇️
airflow/bin/airflow	84.61% <0%> (ø)
airflow/plugins_manager.py	86.95% <0%> (+0.72%)	⬆️
airflow/executors/celery_executor.py	88.51% <0%> (+3.37%)	⬆️
... and 749 more

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