DOC: Correct a typo in comment in .pylintrc

[star1327p]

Correct a typo in comment in .pylintrc: "a if statement" -> "an if statement"

The .pylintrc file in other arviz-devs repositories may also have the same typo.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.52%. Comparing base (bc5a425) to head (9f102ed).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #84   +/-   ##
=======================================
  Coverage   91.52%   91.52%           
=======================================
  Files           6        6           
  Lines         850      850           
=======================================
  Hits          778      778           
  Misses         72       72           

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