CompatHelper: bump compat for MCMCChains to 7, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the MCMCChains package from 5.6, 6 to 5.6, 6, 7.
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.

[bparbhu]

I'm curious where in our github actions do these bots get the command to do this? It's pretty cool just trying to understand how the PR is made.

[bparbhu]

Also looking to understand the build process here as well. I'll look into a CI/CD process for PRs like this. I think this is through the Compathelper script so I'll take a look there first.

[JeffreyBroll]

I also need to know how the CI/CD setup goes but haven't gotten around to it - I'm just going to try not to break .github/workflows in the meantime.

For this specific MR we also have these version requirements in StanSample, so I'm going to test with MCMCChains@7 and that'll need to be updated in both packages - or removed from this one, as it's a dependency of a dependency of Stan.jl and we could probably do without possibly conflicting gizmos.

[bparbhu]

I also need to know how the CI/CD setup goes but haven't gotten around to it - I'm just going to try not to break .github/workflows in the meantime.

For this specific MR we also have these version requirements in StanSample, so I'm going to test with MCMCChains@7 and that'll need to be updated in both packages - or removed from this one, as it's a dependency of a dependency of Stan.jl and we could probably do without possibly conflicting gizmos.

Understood, we'll try and get these sorted this week.

[bparbhu]

I'll take a look at this again this week apologies for the delay.