AIRFLOW-4446 Fix typos detected by github.com/client9/misspell

[andriisoldatenko]

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Jira

• My PR addresses the following "[AIRFLOW-4446] Fix typos detected by github.com/client9/misspell"
  • https://issues.apache.org/jira/browse/AIRFLOW-4446

Description

• Fix few typos.

Code Quality

• Passes flake8

[andriisoldatenko]

cc @ashb

[kaxil]

Thanks @andriisoldatenko

[codecov-io]

Codecov Report

Merging #5217 into master will increase coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #5217      +/-   ##
==========================================
+ Coverage   78.53%   78.53%   +<.01%     
==========================================
  Files         469      469              
  Lines       29965    29972       +7     
==========================================
+ Hits        23533    23540       +7     
  Misses       6432     6432

Impacted Files	Coverage Δ
airflow/contrib/hooks/gcp_vision_hook.py	91.51% <ø> (ø)	⬆️
airflow/contrib/hooks/grpc_hook.py	91.8% <ø> (ø)	⬆️
...contrib/operators/gcp_natural_language_operator.py	100% <ø> (ø)	⬆️
airflow/bin/cli.py	66.83% <0%> (ø)	⬆️
airflow/models/pool.py	96.96% <0%> (+0.81%)	⬆️

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