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/management/commands/load_export.py

@@ -522,7 +522,7 @@ class Command(BaseCommand):
         db_results = self.db.execute(SQL_TABLES_QUERY).fetchall()
         # Database's tables must be a superset of TABLE_NAMES, so we keep compatibility when removing things
         if (missing := TABLE_NAMES - set([table["name"] for table in db_results])):
-            raise CommandError(f"The SQLite database {db_path} miss some expected tables: {sorted(missing)}")
+            raise CommandError(f"The SQLite database {db_path} is missing some expected tables: {sorted(missing)}")
 
         # Check export version
         db_results = self.db.execute(SQL_VERSION_QUERY).fetchall()