[AIRFLOW-5406] allow spark without kubernetes

[tooptoop4]

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• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
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Tests

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Documentation

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[codecov-io]

Codecov Report

Merging #6921 into master will decrease coverage by 0.47%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #6921      +/-   ##
==========================================
- Coverage   84.72%   84.25%   -0.48%     
==========================================
  Files         679      679              
  Lines       38508    38514       +6     
==========================================
- Hits        32626    32450     -176     
- Misses       5882     6064     +182

Impacted Files	Coverage Δ
airflow/contrib/hooks/spark_submit_hook.py	82.11% <50%> (-0.61%)	⬇️
airflow/models/__init__.py	91.3% <50%> (-8.7%)	⬇️
airflow/kubernetes/volume_mount.py	44.44% <0%> (-55.56%)	⬇️
airflow/kubernetes/volume.py	52.94% <0%> (-47.06%)	⬇️
airflow/kubernetes/pod_launcher.py	45.25% <0%> (-46.72%)	⬇️
airflow/executors/sequential_executor.py	56% <0%> (-32%)	⬇️
airflow/kubernetes/refresh_config.py	50.98% <0%> (-23.53%)	⬇️
...rflow/contrib/operators/kubernetes_pod_operator.py	78.75% <0%> (-20%)	⬇️
airflow/utils/dag_processing.py	80.95% <0%> (-7.05%)	⬇️
airflow/utils/sqlalchemy.py	89.83% <0%> (-6.78%)	⬇️
... and 2 more

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