Use tuple for m2m_models

[martimarkov]

Changes how the m2m_models is defined.

Description

Uses a tuple containing the object name and the field.

Related Issue

#1435

Motivation and Context

Ensures that there are no clashes when the m2m relationship is in a parent model and there are multiple child models.

How Has This Been Tested?

Ran all the tests in the suite and no issues came up.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run the pre-commit run command to format and lint.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have added my name and/or github handle to AUTHORS.rst
• I have added my change to CHANGES.rst
• All new and existing tests passed.

[tim-schilling]

Until the tests run for this, we can't move forward with it. This likely means it's blocked by jazzband/help#382

That said, this will need tests confirming the fix from #1435, documentation changes and maybe some way to avoid being backwards incompatible.

[martimarkov]

@tim-schilling so you want me to add tests that cause #1435 as an issue and this to fix them? I'm not sure I'll be able to reproduce it correctly but will think about how to do it

[tim-schilling]

Yes, that's correct. Thank you!