Fix with_variables for TypedPolynomials

[blegat]

No description provided.

[codecov]

Codecov Report

Merging #241 (9a39810) into master (37edbcb) will increase coverage by 0.13%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##           master     #241      +/-   ##
==========================================
+ Coverage   76.70%   76.84%   +0.13%     
==========================================
  Files          36       36              
  Lines        1696     1706      +10     
==========================================
+ Hits         1301     1311      +10     
  Misses        395      395              

Impacted Files	Coverage Δ
src/Certificate/Certificate.jl	97.43% <88.23%> (+0.37%)	⬆️

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