Weird, this works just fine on my install:
[5] pry(main)> message = TestMailer.send_test("test@gmail.com")
TranslationOverride Exists? (0.8ms) SELECT 1 AS one FROM "translation_overrides" WHERE "translation_overrides"."locale" = 'en' AND "translation_overrides"."translation_key" = 'test_mailer.subject_template' LIMIT 1
(0.2ms) SELECT "translation_overrides"."translation_key", "translation_overrides"."value" FROM "translation_overrides" WHERE "translation_overrides"."locale" = 'en'
TestMailer#send_test: processed outbound mail in 259.9ms
=> #<Mail::Message:212740, Multipart: false, Headers: <From: "Discourse" <noreply@unconfigured.discourse.org>>, <Reply-To: "Discourse" <noreply@unconfigured.discourse.org>>, <To: test@gmail.com>, <Subject: [Discourse] Email Deliverability Test>, <Mime-Version: 1.0>, <Content-Type: text/plain>, <X-Auto-Response-Suppress: All>, <Auto-Submitted: auto-generated>>
Since you are using an unsupported-install packaged by Bitnami, it’s expected for it to be broken on subtle ways. We do not support such installs here, so you will want to reach out to their own support channel at Issues · bitnami/charts · GitHub.