Fix finalization of copied arrays.

[maleadt]

This is already part of https://github.com/JuliaGPU/CUDA.jl/pull/438/files, but I want a separate benchmark run before that PR is merged.

[codecov]

Codecov Report

Merging #444 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #444   +/-   ##
=======================================
  Coverage   79.06%   79.06%           
=======================================
  Files         170      170           
  Lines        9275     9277    +2     
=======================================
+ Hits         7333     7335    +2     
  Misses       1942     1942           

Impacted Files	Coverage Δ
src/array.jl	87.76% <100.00%> (+0.17%)	⬆️

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