Steps to reproduce:
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1. create a group G and a grouping H containing group G
2. create an assignment A, with settings "Group mode: separate groups", "Grouping: H" and "Available for group members only: Check"
3. backup the course
4. restore into a new course

What I expected:
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Assignment A in the restored course to be associated with grouping H

What happened:
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Assignment A has no grouping in the restored course