fix: Ignore protected headers in outer message part (#6357)

Delta Chat always adds protected headers to the inner encrypted or signed message, so if a protected
header is only present in the outer part, it should be ignored because it's probably added by the
server or somebody else. The exceptions are Subject and List-ID because there are known cases when
they are only present in the outer message part.

Also treat any Chat-* headers as protected. This fixes e.g. a case when the server injects a
"Chat-Version" IMF header tricking Delta Chat into thinking that it's a chat message.

Also handle "Auto-Submitted" and "Autocrypt-Setup-Message" as protected headers on the receiver
side, this was apparently forgotten.

src/receive_imf/receive_imf_tests.rs

@@ -3682,6 +3682,24 @@ async fn test_unsigned_chat_group_hdr() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_ignore_protected_headers_in_outer_msg() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let bob_chat_id = tcm.send_recv_accept(alice, bob, "hi").await.chat_id;
+    send_text_msg(bob, bob_chat_id, "hi all!".to_string()).await?;
+    let mut sent_msg = bob.pop_sent_msg().await;
+    sent_msg.payload = sent_msg.payload.replace(
+        "Chat-Version:",
+        "Auto-Submitted: auto-generated\r\nChat-Version:",
+    );
+    alice.recv_msg(&sent_msg).await;
+    let ab_contact = alice.add_or_lookup_contact(bob).await;
+    assert!(!ab_contact.is_bot());
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_sync_member_list_on_rejoin() -> Result<()> {
     let mut tcm = TestContextManager::new();