check_verified_properties(): Don't ignore fails of Peerstate::set_verified()

- Return Result from set_verified() so that it can't be missed.
- Pass Fingerprint to set_verified() by value to avoid cloning it inside. This optimises out an
  extra clone() if we already have a value that can be moved at the caller side. However, this may
  add an extra clone() if set_verified() fails, but let's not optimise the fail scenario.

src/securejoin/bobstate.rs

@@ -368,7 +368,7 @@ impl BobState {
         }
         mark_peer_as_verified(
             context,
-            self.invite.fingerprint(),
+            self.invite.fingerprint().clone(),
             mime_message.from.addr.to_string(),
         )
         .await?;