Update pre-commit hooks

[kurtmckee]

This PR introduces the following changes:

• Fix deprecated pre-commit stage names.

  When pre-commit install is run, it currently throws a deprecation regarding the stage names in the config file. This is now fixed.

• Update the pyupgrade hook to its latest version, and update its target syntax version to Python 3.9+.

• Remove flynt as a pre-commit hook.

  Its functionality is handled by the pyupgrade hook.

• Migrate from local pre-commit hooks to standard, hosted pre-commit hooks.

  This change is necessary because not all git-related tooling runs pre-commit hooks with the same activated virtual environment that the Poetry dev dependencies are installed in.

Taken together, these changes bring the pre-commit hook configuration up-to-date, and make it possible to enable pre-commit.ci for the repo if you choose to do so (and I highly recommend doing so!).

[!NOTE]

I've split the commits up so that it can be reviewed commit-by-commit. This isolates the manual and automatic changes so that they can be reviewed in smaller chunks.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 96.66667% with 1 line in your changes missing coverage. Please review. :white_check_mark: Project coverage is 91.91%. Comparing base (49109f7) to head (dfe942b). :warning: Report is 30 commits behind head on master.

Files with missing lines	Patch %	Lines
openapi_spec_validator/validation/protocols.py	50.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #407      +/-   ##
==========================================
- Coverage   92.09%   91.91%   -0.19%     
==========================================
  Files          24       24              
  Lines         759      742      -17     
  Branches       80       83       +3     
==========================================
- Hits          699      682      -17     
+ Misses         42       39       -3     
- Partials       18       21       +3     

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[kurtmckee]

Updated the pre-commit hook versions again.

[kurtmckee]

Happy new year, @p1c2u! I hope you're well! Would you take a look at this and the other PRs I've posted? I'd like to help ensure that the project infrastructure is up-to-date and functional, to help make the project more maintainable. :+1: