fix: always specify encoding

[lars-reimann]

Summary of Changes

Always specify the encoding when opening files.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	black	3	0	0	0.55s
✅ PYTHON	mypy	3		0	5.55s
✅ PYTHON	ruff	3	0	0	0.03s
✅ REPOSITORY	git_diff	yes		no	0.03s

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.55%. Comparing base (aec4abd) to head (1f0a5a2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #135   +/-   ##
=======================================
  Coverage   99.55%   99.55%           
=======================================
  Files          25       25           
  Lines        2477     2477           
=======================================
  Hits         2466     2466           
  Misses         11       11           

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