fix many-to-many Propel1 ModelChoiceList
merged branch havvg/2.2 (PR #8240)

This PR was merged into the 2.2 branch.

Discussion
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[Propel1] fix many-to-many Propel1 ModelChoiceList

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

replaces #8223

Commits
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25e3abd fix many-to-many Propel1 ModelChoiceList