CompatHelper: bump compat for Libtask to 0.6, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Libtask package from 0.4, 0.5.3 to 0.4, 0.5.3, 0.6.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov]

Codecov Report

Merging #1767 (aa8181f) into master (45bbea9) will increase coverage by 0.63%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1767      +/-   ##
==========================================
+ Coverage   81.23%   81.87%   +0.63%     
==========================================
  Files          24       24              
  Lines        1471     1473       +2     
==========================================
+ Hits         1195     1206      +11     
+ Misses        276      267       -9     

Impacted Files	Coverage Δ
src/inference/hmc.jl	79.39% <100.00%> (+3.03%)	⬆️
src/inference/AdvancedSMC.jl	97.47% <0.00%> (+0.04%)	⬆️
src/essential/ad.jl	86.07% <0.00%> (+5.06%)	⬆️

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[yebai]

Closed in favour of #1766