Test cleanup

[t-bltg]

Remove spurious display of UnicodePlots plots during testing.

[codecov]

Codecov Report

Merging #3821 (ecc76eb) into master (cd6a8c8) will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3821      +/-   ##
==========================================
+ Coverage   62.97%   63.02%   +0.05%     
==========================================
  Files          28       28              
  Lines        7467     7467              
==========================================
+ Hits         4702     4706       +4     
+ Misses       2765     2761       -4     

Impacted Files	Coverage Δ
src/backends/unicodeplots.jl	41.40% <0.00%> (-3.91%)	⬇️
src/recipes.jl	59.71% <0.00%> (+0.10%)	⬆️
src/utils.jl	54.93% <0.00%> (+0.15%)	⬆️
src/plot.jl	71.03% <0.00%> (+4.82%)	⬆️

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