fix(docs): Fix broken docs generation

[michalbil]

Description

Update m2r package version to 0.3.1, done by executing:

poetry add -G dev m2r@^0.3.1

Motivation and Context

Resolves #552

How Has This Been Tested?

By executing poetry run make docs.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes if appropriate.
• [ ] All new and existing tests passed.