cubicweb-vcreview #2924070 migration to 1.0.0 can break on repository_committer/repository_reviewer relations [validation pending]

If "R has_patch_repository PR, R repository_committer U, PR repository_committer U", the migration will try to create a duplicate R repository_committer U relation. Same with repository_reviewer.

done in1.2.0
load left0.000
closed by#1ee611c523f4 Be more careful in 1.0.0 migration (closes #2924070)
patchBe more careful in 1.0.0 migration [applied]