Add emphasis on ActiveRecord Encryption configuration values being secret (#30340)

config/initializers/active_record_encryption.rb

@@ -5,7 +5,7 @@
   ACTIVE_RECORD_ENCRYPTION_KEY_DERIVATION_SALT
   ACTIVE_RECORD_ENCRYPTION_PRIMARY_KEY
 ).each do |key|
-  ENV.fetch(key) do
+  value = ENV.fetch(key) do
     abort <<~MESSAGE
 
       Mastodon now requires that these variables are set:
@@ -14,9 +14,18 @@
         - ACTIVE_RECORD_ENCRYPTION_KEY_DERIVATION_SALT
         - ACTIVE_RECORD_ENCRYPTION_PRIMARY_KEY
 
-      Run `bin/rails db:encryption:init` to generate values and then assign the environment variables.
+      Run `bin/rails db:encryption:init` to generate new secrets and then assign the environment variables.
     MESSAGE
   end
+
+  next unless Rails.env.production? && value.end_with?('DO_NOT_USE_IN_PRODUCTION')
+
+  abort <<~MESSAGE
+
+    It looks like you are trying to run Mastodon in production with a #{key} value from the test environment.
+
+    Please generate fresh secrets using `bin/rails db:encryption:init` and use them instead.
+  MESSAGE
 end
 
 Rails.application.configure do