Trac ticket number

ticket-35453

Branch description

This change ensures that ManyToManyField.concrete returns False, reflecting the fact that M2M fields do not correspond to a concrete database column. This aligns with expectations and avoids confusion when introspecting model fields.

A new test was added to assert that .concrete is False for M2M fields.

To support this behavior without breaking model field setup (where .concrete is unconditionally assigned), a property with a no-op setter was used that forces concrete to remain False even when Django tries to assign to it.

This avoids a crash during model initialization and ensures that schema-related logic (e.g., field lateration checks) treat M2M fields correctly.

Checklist

• This PR targets the main branch.
• The commit message is written in past tense, mentions the ticket number, and ends with a period.
• I have checked the "Has patch" ticket flag in the Trac system.
• I have added or updated relevant tests.
• I have added or updated relevant docs, including release notes if applicable.
• I have attached screenshots in both light and dark modes for any UI changes.