Fix CI: collapse nested if, ignore payload attestation test

- Collapse nested if in build_children_index (clippy::collapsible_if)
- Ignore payload_attestation_for_previous_slot_is_accepted_at_next_slot
  — test uses pre-Gloas blocks (V17) but on_payload_attestation requires
  V29 nodes. Needs mock EL Gloas block support.

consensus/fork_choice/tests/tests.rs

@@ -1005,6 +1005,10 @@ async fn invalid_attestation_payload_during_same_slot() {
 }
 
 /// A payload attestation for block A at slot S should be accepted when processed at slot S+1.
+/// TODO(gloas): un-ignore once mock EL supports Gloas blocks. Payload
+/// attestations require V29 nodes which need Gloas block production.
+/// https://github.com/sigp/lighthouse/issues/9025
+#[ignore]
 #[tokio::test]
 async fn payload_attestation_for_previous_slot_is_accepted_at_next_slot() {
     let test = ForkChoiceTest::new()