v4.0: Ignores ancestors in snapshot (backport of #10835)

[mergify]

Problem

Loading from a snapshot doesn't require reading the ancestors.

Summary of Changes

Ignore 'em.

Justification to Backport

This one isn't a big deal, no, and we don't need to backport it. But it does impact other snapshot changes I'm making due to how frozen abi stuff works. There are other PRs after this one that I intend to backport to v4.0 as well. By backporting this one, and all the subsequent ones, and doing them all in order, that ensures each one will have a clean diff. Otherwise the frozen abi digest will differ each time, requiring manual intervention.

---

This is an automatic backport of pull request #10835 done by [Mergify](https://mergify.com).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.0%. Comparing base (d9b792f) to head (8bf0621).

Additional details and impacted files

@@            Coverage Diff            @@
##             v4.0   #10990     +/-   ##
=========================================
- Coverage    83.0%    83.0%   -0.1%     
=========================================
  Files         836      836             
  Lines      316382   316380      -2     
=========================================
- Hits       262780   262738     -42     
- Misses      53602    53642     +40     

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