Use group organization for user personal namespace
What does this MR do and why?
During my work on !155732 (merged), I noticed a new failure in the pipelines. In that MR, we will ensure a namespace has an organization.
The failure was caused because the default organization does not exist in this test. But in this case, it makes more sense to assign the Group organization to the User namespace.
So this MR will change that: the newly created import user will have the same organization as the top level group.
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Related to #411832