make MCMCThreads etc. respect check_model=false

[penelopeysm]

Prior to this PR, if you called

sample(model, spl, MCMCThreads(), N, n; check_model=false)

the model checking here

Turing.jl/src/mcmc/abstractmcmc.jl

Line 121 in ed7f76c

check_model && _check_model(model, spl)

would be correctly skipped. The problem is that this calls AbstractMCMC.mcmcsample, which then calls the single-threaded sample, but the check_model argument is not passed down, so it defaults to true which then checks the model(!!)

This PR fixes it by simply passing check_model=false through. (The point of explicitly setting it to false is that if the user wanted the check, it would be done on the line above already, there's no need to check the model N+1 times.)

The added test fails on main and passes on this PR.

[github-actions]

Turing.jl documentation for PR #2721 is available at:
https://TuringLang.github.io/Turing.jl/previews/PR2721/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.80%. Comparing base (ed7f76c) to head (7a64206).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2721   +/-   ##
=======================================
  Coverage   86.80%   86.80%           
=======================================
  Files          22       22           
  Lines        1455     1455           
=======================================
  Hits         1263     1263           
  Misses        192      192           

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