Fix doc typo to make code block instead of block quote

[mjsir911]

Description

Fix small rst typo

Related Issue

Motivation and Context

Makes the intended code block rather than one-line block quote

How Has This Been Tested?

It's rendered correctly in https://github.com/mjsir911/django-simple-history/blob/msirabella/typo_code_block/CONTRIBUTING.rst#code-formatting

Screenshots (if appropriate):

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 run the pre-commit run command to format and lint.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have added my name and/or github handle to AUTHORS.rst
• I have added my change to CHANGES.rst
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #1185 (13cdf3c) into master (5128890) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1185   +/-   ##
=======================================
  Coverage   97.30%   97.30%           
=======================================
  Files          23       23           
  Lines        1262     1262           
  Branches      204      199    -5     
=======================================
  Hits         1228     1228           
  Misses         16       16           
  Partials       18       18           

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[ddabble]

Thank you! 😊