archiver: Clarify value in test struct
archiver: Clarify value in test struct

Since I could not remember what the value for `Check` means this commit
renames it to `SameFile`: when set to true, the test should make sure
that `FileChanged` should return false (=file is unmodified).

restic/restic,middelink/restic,middelink/restic,restic/restic