Fix pylint error

[awdeorio]

Fix errors due to changes in pylint pylint-dev/pylint#9099

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 99.74%. Comparing base (8b3024a) to head (4a6af96).
Report is 9 commits behind head on develop.

Files with missing lines	Patch %	Lines
mailmerge/__main__.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #161   +/-   ##
========================================
  Coverage    99.74%   99.74%           
========================================
  Files            5        5           
  Lines          391      391           
========================================
  Hits           390      390           
  Misses           1        1           

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