How to reproduce:
1. Open the user's attached "UnityPathfindingTesting" project
2. Open the "PathfindingTesting" Scene
3. Enable "Show NavMesh" at the bottom right of the Scene view if it's disabled
4. Observe the "NavmeshArtifact" GameObject's bottom of the stairs part in the Scene view

Expected results: NavMesh is stretched between the voxel tile edge and the stairs
Actual results: NavMesh is not stretched between the voxel tile edge and the stairs

Reproducible with: 2018.4.29f1, 2019.4.14f1, 2020.1.13f1, 2020.2.0b11, 2021.1.0a5

Notes:
- The NavMesh becomes stretched when one of the steps is either higher than step height or roughly 30% wider than the previous step, length doesn't seem to have any effect