[veggies] Fix bump map of the yellow bell pepper

[DamrongGuoy]

With help from @SeanCurtis-TRI, we fix the visual effect of the bump map of the yellow bell pepper in MeshCat.

These two pictures from MeshCat compare the effect before and after this change.

The companion Drake PR is https://github.com/RobotLocomotion/drake/pull/20485. From that Drake PR, you can run Drake with:

drake $ bazel run //examples/hydroelastic/python_nonconvex_mesh:drop_pepper_py -- --simulation_time=0

---

This change is 

[jwnimmer-tri]

(given https://github.com/RobotLocomotion/drake/pull/20485#pullrequestreview-1717701805).