Fix PII scrubbing for untyped standalone attachments

Use unwrap_or_default() to treat attachments without an explicit
AttachmentType header as AttachmentType::Attachment, ensuring they
are correctly routed to the StandaloneAttachments processing group
for PII scrubbing instead of falling through to the Standalone group.

Author: cursoragent

relay-server/src/services/processor.rs

@@ -380,7 +380,7 @@ impl ProcessingGroup {
         if !envelope.items().any(Item::creates_event) {
             let standalone_attachments = envelope.take_items_by(|i| {
                 i.requires_event()
-                    && matches!(i.attachment_type(), Some(AttachmentType::Attachment))
+                    && i.attachment_type().unwrap_or_default() == AttachmentType::Attachment
             });
             if !standalone_attachments.is_empty() {
                 grouped_envelopes.push((