DEPR: enforce deprecation MultiIndex.is_lexsorted and MultiIndex.lexsort_depth
- [x] Added an entry in the latest `doc/source/whatsnew/v2.0.0.rst` file if fixing a bug or adding a new feature.

Deprecation introduced in #38701
> Doc build fails

fixed and now green. thx thx @lukemanley (can you update deprecations issue?)