Set `{{ matrix_admin if matrix_admin else '' }}` to `matrix_zulip_bridge_owner`

Signed-off-by: Suguru Hirahara <did🔑z6MkvVZk1A3KBApWJXv2Ju4H14ErDfRGxh8zxdXSZ4vACDg5>

roles/custom/matrix-bridge-zulip/defaults/main.yml

@@ -27,7 +27,7 @@ matrix_zulip_bridge_docker_image_registry_prefix_upstream_default: ghcr.io/
 matrix_zulip_bridge_docker_image_force_pull: "{{ matrix_zulip_bridge_docker_image.endswith(':latest') }}"
 
 # Set this to your Matrix ID if you want to enforce the owner, otherwise first _local_ user becomes one
-matrix_zulip_bridge_owner: ""
+matrix_zulip_bridge_owner: "{{ matrix_admin if matrix_admin else '' }}"
 
 matrix_zulip_bridge_base_path: "{{ matrix_base_data_path }}/zulip"