style: end the new corpus files with a single newline

CI's diff-hygiene gate rejects a trailing blank line at EOF; the local
check:diff run happened before the first commit existed, so it checked the
previous range and missed it.

scripts/corpus_manifest.py

@@ -239,4 +239,3 @@ def revoke(dataset_root: Path, contribution_id: str, at: str, reason: str) -> di
     }
     append_record(manifest_path, tombstone)
     return tombstone
-

tests/corpus-manifest.test.py

@@ -271,5 +271,3 @@ class IllegalTransitionTests(unittest.TestCase):
 
 if __name__ == "__main__":
     unittest.main(verbosity=2)
-
-