CompatHelper: bump compat for OrderedCollections to 2, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the OrderedCollections package from 1.8.1 to 1.8.1, 2.
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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.46%. Comparing base (9ebf18f) to head (244f25e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #169      +/-   ##
==========================================
- Coverage   89.39%   84.46%   -4.93%     
==========================================
  Files          16       16              
  Lines        1056     1056              
==========================================
- Hits          944      892      -52     
- Misses        112      164      +52     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[github-actions]

AbstractPPL.jl documentation for PR #169 is available at:
https://TuringLang.github.io/AbstractPPL.jl/previews/PR169/