don't leak a file descriptor to os.devnull by default

[asottile]

since this is passed along to subprocess directly we can use the subprocess constants still

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Description

avoid one open call without a close -- this doesn't fix the other one in the file but I am less concerned with that one since I am only using the default behaviour

I also adjusted is to == for the subprocess constants -- they are not guaranteed to be singletons so they should be compared with equality

Motivation and Context

regression in #12103

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation. N/A
• I have updated the documentation accordingly. N/A
• I have added tests to cover my changes. N/A
• All new and existing tests passed.

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All committers have signed the CLA.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (354c718) 57.52% compared to head (32b0a60) 57.52%.
Report is 2 commits behind head on trunk.

❗ Current head 32b0a60 differs from pull request most recent head df054db. Consider uploading reports for the commit df054db to get more accurate results

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Additional details and impacted files

@@           Coverage Diff           @@
##            trunk   #13162   +/-   ##
=======================================
  Coverage   57.52%   57.52%           
=======================================
  Files          86       86           
  Lines        5299     5299           
  Branches      221      221           
=======================================
  Hits         3048     3048           
  Misses       2030     2030           
  Partials      221      221           

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[titusfortner]

Thank you!