fix types, Model.schema() return wrong type.

[Hrysa]

Pull Request check-list

Please make sure to review and check all of these items:

• Does npm run test or npm run test-DIALECT pass with this change (including linting)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving?
• Have you added new tests to prevent regressions?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Did you follow the commit message conventions explained in CONTRIBUTING.md?

Description of change

[codecov]

Codecov Report

Merging #10624 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #10624   +/-   ##
=======================================
  Coverage   96.18%   96.18%           
=======================================
  Files          93       93           
  Lines        9011     9011           
=======================================
  Hits         8667     8667           
  Misses        344      344

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d81ea5e...517163d. Read the comment docs.

[sushantdhiman]

🎉 This PR is included in version 5.2.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀