Truncated suppressions table

We have been adding emails to the suppressions table which are not on
the suppression list in Mailgun due to a misunderstanding of how
Mailgun handles 5xx error codes.

ghost/core/core/server/data/migrations/versions/5.29/2023-01-11-02-45-truncate-suppressions.js

@@ -0,0 +1,12 @@
+const logging = require('@tryghost/logging');
+const {createNonTransactionalMigration} = require('../../utils');
+
+module.exports = createNonTransactionalMigration(
+    async function up(knex) {
+        logging.info('Clearing suppressions table');
+        await knex('suppressions').truncate();
+    },
+    async function down() {
+        logging.info('Not doing anything - table has been truncated');
+    }
+);