Move constant to set in psdt2

[blegat]

Otherwise, sets that do not support nonzero constant in ScalarAffineFunction will fail the test

[codecov-io]

Codecov Report

Merging #622 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #622   +/-   ##
=======================================
  Coverage   95.19%   95.19%           
=======================================
  Files          48       48           
  Lines        5080     5080           
=======================================
  Hits         4836     4836           
  Misses        244      244

Impacted Files	Coverage Δ
src/Test/contconic.jl	100% <100%> (ø)	⬆️

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