[AIRFLOW-5497] Update docstring with param description

[chicochico]

Make sure you have checked all steps below.

Jira

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  • https://issues.apache.org/jira/browse/AIRFLOW-XXX
  • In case you are fixing a typo in the documentation you can prepend your commit with [AIRFLOW-XXX], code changes always need a Jira issue.
  • In case you are proposing a fundamental code change, you need to create an Airflow Improvement Proposal (AIP).
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Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason: Documentation change

Commits

• My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
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  6. Body explains "what" and "why", not "how"

[BasPH]

Looks good. Tests seem flaky so I restarted the failed tests.

[codecov-io]

Codecov Report

Merging #6314 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6314      +/-   ##
==========================================
- Coverage   80.34%   80.34%   -0.01%     
==========================================
  Files         616      616              
  Lines       35733    35737       +4     
==========================================
+ Hits        28711    28712       +1     
- Misses       7022     7025       +3

Impacted Files	Coverage Δ
airflow/utils/dag_processing.py	56.37% <ø> (-0.52%)	⬇️
airflow/gcp/operators/bigquery.py	86.44% <0%> (-0.17%)	⬇️
airflow/gcp/operators/mlengine.py	89.51% <0%> (ø)	⬆️
airflow/config_templates/airflow_local_settings.py	80.48% <0%> (+0.48%)	⬆️
airflow/gcp/hooks/mlengine.py	83.73% <0%> (+1.04%)	⬆️
airflow/operators/redshift_to_s3_operator.py	97.14% <0%> (+1.58%)	⬆️

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