Prepare 4.2.1

[phil-davis]

I will do a patch release for this tiny thing. Then we can think about merging other PRs like #1365 (which is #1290 rebased)... and doing a minor release bump.

[codecov]

Codecov Report

Merging #1372 (2d92231) into master (f8c1acc) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1372   +/-   ##
=========================================
  Coverage     97.35%   97.35%           
  Complexity     2810     2810           
=========================================
  Files           174      174           
  Lines          7978     7978           
=========================================
  Hits           7767     7767           
  Misses          211      211           

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