Bump DynamicPPL compat to 0.31

[penelopeysm]

DPPL 0.31 was mostly internal changes to context testing inside DynamicPPL.TestUtils, so shouldn't affect anything in Turing (Turing doesn't use any of those functions). This is just a boring version bump to keep Turing up to date.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.41%. Comparing base (f3b2476) to head (41eebbb).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2404   +/-   ##
=======================================
  Coverage   86.41%   86.41%           
=======================================
  Files          22       22           
  Lines        1575     1575           
=======================================
  Hits         1361     1361           
  Misses        214      214           

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[coveralls]

Pull Request Test Coverage Report for Build 12090970287

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 78.585%

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Totals
Change from base Build 12082865030:	0.0%
Covered Lines:	1233
Relevant Lines:	1569

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💛 - Coveralls