Possible inconsistency for undefined texture sampler handling

The text at https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#textures says

> When `texture.sampler` is undefined, a sampler with repeat wrapping (in both directions) and auto filtering **MUST** be used.

The properties reference at https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#reference-texture says about the sampler

> The index of the sampler used by this texture. When undefined, a sampler with repeat wrapping and auto filtering **SHOULD** be used.

I think that this **MUST** vs. **SHOULD** is an inconsistency.

Read the textures and reference-texture sections linked in the issue and compare their requirements for an undefined texture.sampler. Decide which MUST or SHOULD wording is correct, update the inconsistent specification text, and verify that both sections use the same requirement.

Written by the indexing model from the issue text.