fix handling of ^ in bagof/3, setof/3.

[ichiban]

#223

[codecov]

Codecov Report

Merging #232 (fe46b69) into main (75737ad) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #232      +/-   ##
==========================================
+ Coverage   97.42%   97.46%   +0.04%     
==========================================
  Files          21       21              
  Lines        6669     6700      +31     
==========================================
+ Hits         6497     6530      +33     
+ Misses        140      138       -2     
  Partials       32       32              

Impacted Files	Coverage Δ
engine/env.go	98.10% <ø> (-0.17%)	⬇️
engine/builtin.go	96.77% <100.00%> (-0.05%)	⬇️
engine/term.go	100.00% <100.00%> (ø)
engine/variable.go	100.00% <100.00%> (+5.26%)	⬆️

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