height reference accounts for change in terrain provider test failure in CI

[lukemckinstry]

What happened?

Test failed in CI as follows
First time I hit "re-run failed jobs" it then passed
submitting this error to help document if this is a flakey test that fails often

Reproduction steps

1. Happened when CI ran for commit 165e0fb unreleated to the the tested code that failed, in the coverage CI step
2. can rerun tests locally with npm run coverage, but was unable to reproduce this failure locally

Sandcastle example

No response

Environment

CI in Github

[lukemckinstry]

this occurred again for me just now on this CI run (same PR branch as before) https://github.com/CesiumGS/cesium/actions/runs/10885450028/job/30203094050?pr=12193