Relax the compat entry for MCMCChains

[astrozot]

Version 7 of MCMCChains has a very minor breaking change: it just redefines the display of a chain, so that no summary information is shown anymore. Therefore, this version actually works without issues with Pigeons.

https://github.com/TuringLang/MCMCChains.jl/releases

I propose therefore to change the compat entry for MCMCChains into

MCMCChains = "6", "7"

[astrozot]

Dear all, I hope someone is reading this and approves the pull request I made: it is really a minor thing but it blocks a series of package updates in my project. Thank you!

[alexandrebouchard]

Apologies. Sounds good, I have started the CI workflow runs!

[alexandrebouchard]

After that sounds good to merge. We should do a new version release soon.

[astrozot]

Thank you, looking forward for the new release!