PR that marks the test: #137812

Steps to repro:

1. Add LeakTesting.settings = LeakTesting.settings.withTracked(allNotGCed: true); as first line in main of flutter/test/rendering/viewport_test.dart
2. Remove withIgnored for some tests added by the PR above
3. See the test failing

Also test with --test-randomize-ordering-seed=20231114.

notGCed leaks are not enabled for the library, because the leaks are flacky.