S2Cell test failure

### What happened?

The following spec is failing in CI on the `main` branch.

It seems to have originated in this PR https://github.com/CesiumGS/cesium/pull/13581#pullrequestreview-4664583545
but the reason is not clear why as it did not seem to involve relevant code changes.

```
Core/S2Cell
✗ gets correct center of cell
Expected (-1691083.4101336685, 6039960.550535122, -1153592.7688487188) to equal epsilon (-1691083.4101336703, 6039960.550535122, -1153592.7688487188), 1e-15.
at
at UserContext. (packages/engine/Specs/Core/S2CellSpec.js:294:62 <- Build/Specs/SpecList.js:157538:74)
at

2.006 secs: Scene/Scene flyTo camera after morph to CV
1.74 secs: Core/createWorldBathymetryAsync resolves to CesiumTerrainProvider instance with default parameters
1.508 secs: Scene/Scene flyTo camera after morph to 2D
1.332 secs: Scene/Cesium3DTileset Restrict tileset memory usage with maximumCacheOverflowBytes
1.186 secs: Core/TaskProcessor works with a simple worker
1.02 secs: DataSources/KmlDataSource NetworkLink: onInterval
1.005 secs: Scene/Scene flyTo camera after morph to 3D
0.921 secs: Scene/GroundPrimitive larger scene renders batched instances
0.885 secs: Scene/GaussianSplat3DTileContent Load multiple instances of Gaussian splat tileset and validate transformed attributes
0.84 secs: DataSources/PolygonGeometryUpdater Computes dynamic geometry bounding sphere for fill.

Chrome Headless 150.0.0.0 (Linux 0.0.0): Executed 15614 of 15687 (1 FAILED) (skipped 73) (1 min 2.877 secs / 57.397 secs)
TOTAL: 1 FAILED, 15613 SUCCESS

1) gets correct center of cell
Core/S2Cell
Expected (-1691083.4101336685, 6039960.550535122, -1153592.7688487188) to equal epsilon (-1691083.4101336703, 6039960.550535122, -1153592.7688487188), 1e-15.
at
at UserContext. (packages/engine/Specs/Core/S2CellSpec.js:294:62 <- Build/Specs/SpecList.js:157538:74)
at

TOTAL: 1 FAILED, 15613 SUCCESS
[14:32:55] 'test' errored after 1.35 min
[14:32:55] Error: 1
at formatError (/home/runner/work/cesium/cesium/node_modules/gulp-cli/lib/versioned/^5.0.0/format-error.js:21:10)
at Gulp. (/home/runner/work/cesium/cesium/node_modules/gulp-cli/lib/versioned/^5.0.0/log/events.js:33:54)
at Gulp.emit (node:events:531:35)
at Gulp.emit (node:domain:489:12)
at Object.error (/home/runner/work/cesium/cesium/node_modules/undertaker/lib/helpers/createExtensions.js:61:10)
at handler (/home/runner/work/cesium/cesium/node_modules/now-and-later/lib/map.js:68:20)
at f (/home/runner/work/cesium/cesium/node_modules/once/once.js:25:25)
at f (/home/runner/work/cesium/cesium/node_modules/once/once.js:25:25)
at tryCatch (/home/runner/work/cesium/cesium/node_modules/async-done/index.js:21:15)
at done (/home/runner/work/cesium/cesium/node_modules/async-done/index.js:37:12)
Error: Process completed with exit code 1.

```

### Reproduction steps

1. Occurring in CI on `main` branch
2.
3.
...

### Sandcastle example

_No response_

### Environment

Browser:
CesiumJS Version:
Operating System:

### AI acknowledgment

- [ ] I used AI to generate this issue report.
- [ ] (If the above is checked) I have reviewed the AI-generated content before submitting.

Start with packages/engine/Specs/Core/S2CellSpec.js at line 294 and reproduce the Core/S2Cell failure in CI. Compare the change history around PR 13581 to identify why the computed center differs by a tiny amount, then verify the intended result by rerunning the spec and the full test suite.

Written by the indexing model from the issue text.