fix buscarron ban list

roles/matrix-bot-buscarron/templates/env.j2

@@ -10,7 +10,7 @@ BUSCARRON_SPAM_LOCALPARTS={{ matrix_bot_buscarron_spam_localparts|join(" ") }}
 BUSCARRON_SENTRY={{ matrix_bot_buscarron_sentry }}
 BUSCARRON_LOGLEVEL={{ matrix_bot_buscarron_loglevel }}
 BUSCARRON_BAN_SIZE={{ matrix_bot_buscarron_ban_size }}
-BUSCARRON_BAN_LIST={{ matrix_bot_buscarron_ban_list }}
+BUSCARRON_BAN_LIST={{ matrix_bot_buscarron_ban_list|default('')|join(' ') }}
 BUSCARRON_PM_TOKEN={{ matrix_bot_buscarron_pm_token }}
 BUSCARRON_PM_FROM={{ matrix_bot_buscarron_pm_from }}
 BUSCARRON_PM_REPLYTO={{ matrix_bot_buscarron_pm_replyto }}