Exclude .coverage.py from linting

[zidder]

Brief summary of the change made

fixes #3563
Because of the .coverage.py file, the linting raised this kind of error:

ValueError: source code string cannot contain null bytes
ERROR: InvocationError for command /home/zidder/pythonTricks/sqlfluff/.tox/linting/bin/flake8 (exited with code 1)

Now this error is gone, because the .coverage.py is not linted anymore.

Are there any other side effects of this change that we should be aware of?

Pull Request checklist

• Please confirm you have completed any of the necessary steps below.

• Included test cases to demonstrate any code changes, which may be one or more of the following:

  • .yml rule test cases in test/fixtures/rules/std_rule_cases.
  • .sql/.yml parser test cases in test/fixtures/dialects (note YML files can be auto generated with tox -e generate-fixture-yml).
  • Full autofix test cases in test/fixtures/linter/autofix.
  • Other.

• Added appropriate documentation for the change.

• Created GitHub issues for any relevant followup/future enhancements if appropriate.

[codecov]

Codecov Report

Merging #3564 (6a236fa) into main (b1a13a5) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main     #3564   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          172       172           
  Lines        13083     13083           
=========================================
  Hits         13083     13083           

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[barrywhart]

Good catch. Thanks for the fix!