Tidy up tests workflow

[ericpre]

Remove installing traits development version when testing python 3.13, now that the traits release supports python 3.13.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.84%. Comparing base (a89cb09) to head (a0bfd9e).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #363   +/-   ##
=======================================
  Coverage   87.84%   87.84%           
=======================================
  Files          85       85           
  Lines       11246    11246           
  Branches     2084     2084           
=======================================
  Hits         9879     9879           
  Misses        868      868           
  Partials      499      499           

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