Pass aggregate.committee_bits to get_committee_indices (#4742)

Correct the beacon_aggregate_and_proof validation to call
get_committee_indices(aggregate.committee_bits) instead of
get_committee_indices(aggregate). Electra defines get_committee_indices
to accept a committee bitvector and all related code paths and tests use
.committee_bits. This change aligns the networking spec with the Electra
attestation format introduced by EIP-7549 and avoids implementer
confusion.

Author: GarmashAlex

specs/electra/p2p-interface.md

@@ -98,14 +98,16 @@ The derivation of the `message-id` remains stable.
 
 ###### `beacon_aggregate_and_proof`
 
-The following convenience variables are re-defined
+Assuming the alias `aggregate = signed_aggregate_and_proof.message.aggregate`:
+
+The following convenience variables are re-defined:
 
 - `index = get_committee_indices(aggregate.committee_bits)[0]`
 
 The following validations are added:
 
 - [REJECT] `len(committee_indices) == 1`, where
-  `committee_indices = get_committee_indices(aggregate)`.
+  `committee_indices = get_committee_indices(aggregate.committee_bits)`.
 - [REJECT] `aggregate.data.index == 0`
 
 ###### `blob_sidecar_{subnet_id}`