Support exports version 8 in the load_export command

Closes #1762 (closed)

Tested by importing this v8 export from this Horae dump from PictorIA workshop.

arkindex/documents/tests/commands/test_load_export.py

@@ -100,7 +100,13 @@ class TestLoadExport(FixtureTestCase):
         _, temp_file = tempfile.mkstemp(suffix=".db")
         with self.assertRaises(CommandError) as context:
             call_command("load_export", temp_file, "--email", self.user.email)
-        self.assertEqual(str(context.exception), f"The SQLite database {temp_file} is not a correct Arkindex export")
+        self.assertEqual(str(context.exception), (
+            f"The SQLite database {temp_file} miss some expected tables: "
+            "['classification', 'dataset', 'dataset_element', 'element', "
+            "'element_path', 'entity', 'entity_type', 'export_version', "
+            "'image', 'image_server', 'metadata', 'transcription', "
+            "'transcription_entity', 'worker_run', 'worker_version']"
+        ))
 
     def test_invalid_version(self):
         _, temp_file = tempfile.mkstemp(suffix=".db")
@@ -113,7 +119,7 @@ class TestLoadExport(FixtureTestCase):
 
         with self.assertRaises(CommandError) as context:
             call_command("load_export", temp_file, "--email", self.user.email, "--corpus-name", "My corpus")
-        self.assertEqual(str(context.exception), f"The SQLite database {temp_file} does not have the correct export version")
+        self.assertEqual(str(context.exception), f"The SQLite database {temp_file} does not have a supported export version")
 
     @patch("arkindex.documents.export.os.unlink")
     @patch("arkindex.project.aws.s3.Object")