test/unit/merge: Wrap #migrateFileid() test in describe block
test/unit/merge: Wrap #migrateFileid() test in describe block

To make it easier to add more cases.
This commit is almost only about indenting stuff.

cozy-labs/cozy-desktop,cozy-labs/cozy-desktop,cozy-labs/cozy-desktop,cozy-labs/cozy-desktop