add missing electra attestation processing committee check

[mehdi-aouadi]

PR Description

Add missing committee attester check when processing Electra attestations:
https://github.com/ethereum/consensus-specs/blob/31cd9cbec2d93e5a6df84dcee9ca9e8aa77803ee/specs/electra/beacon-chain.md?plain=1#L1330

Fixed Issue(s)

fixes #8892

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[tbenr]

humm looks like we do things slightly differently there.. for instance where is assert len(attestation.aggregation_bits) == committee_offset?

[mehdi-aouadi]

humm looks like we do things slightly differently there.. for instance where is assert len(attestation.aggregation_bits) == committee_offset?

That's done:

if (participantsCount != aggregationBits.size()) {
      return Optional.of(AttestationInvalidReason.PARTICIPANTS_COUNT_MISMATCH);
    }

https://github.com/ConsenSys/teku/blob/8f291ea277a3ace4e1aee6e9c388cc6e325efedc/ethereum/spec/src/main/java/tech/pegasys/teku/spec/logic/versions/electra/block/BlockProcessorElectra.java#L748-L750

As discussed, I'll push some other changes to make it more aligned with the spec.

[tbenr]

LGTM. Just a var name suggestion