Regression test for #906

[mdickinson]

Do not merge: this is an example regression test for #906. If it fails in the expected way, I'll merge this branch into the branch for #907.

[mdickinson]

Yay! Expected segfaults all around.

[codecov-io]

Codecov Report

Merging #910 into master will increase coverage by 0.29%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #910      +/-   ##
==========================================
+ Coverage   72.59%   72.89%   +0.29%     
==========================================
  Files          51       51              
  Lines        6474     6474              
  Branches     1302     1302              
==========================================
+ Hits         4700     4719      +19     
+ Misses       1378     1355      -23     
- Partials      396      400       +4

Impacted Files	Coverage Δ
traits/editor_factories.py	81.25% <0%> (-3.13%)	⬇️
traits/trait_types.py	71.07% <0%> (-0.16%)	⬇️
traits/has_traits.py	70.72% <0%> (+0.33%)	⬆️
traits/traits.py	76.92% <0%> (+4.04%)	⬆️
traits/etsconfig/etsconfig.py	63.8% <0%> (+6.13%)	⬆️

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