Split from #3407 (GitHub milestones on migration): a builder left it without a pull because the carry and the membership were one change. This puts carried issues and pulls in their milestones.
Done:
[ ] Each carried issue and pull that belonged to a GitHub milestone belongs to the matching forge milestone.
[ ] A second migration does not add it twice.
[ ] Test: 3 issues across the 2 seeded milestones land in the right ones.
Split from #3407 (GitHub milestones on migration): a builder left it without a pull because the carry and the membership were one change. This puts carried issues and pulls in their milestones.
Done:
Files: the GitHub carry module, the migrate test.