message: fix issue in data migration constructor
diff: @@ -18,7 +18,7 @@ use crate::{
  };
  // This will be changed in favour of an actual old config type when the migration is not a no-op.
  -type OldConfig = Config;
  +type OldConfig = toml::Value;
  /// The name of the file for recording the new global state hash after a data migration.
  const POST_MIGRATION_STATE_HASH_FILENAME: &str = "post-migration-state-hash";
  