Release 4.2.1

[sliverc]

Description of the Change

Prepare bugfix release 4.2.1

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #958 (c9d40b6) into master (b49aa6e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #958   +/-   ##
=======================================
  Coverage   96.81%   96.81%           
=======================================
  Files          64       64           
  Lines        3888     3888           
=======================================
  Hits         3764     3764           
  Misses        124      124           

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