Missing defer before unlock (#5643)

* missing defer before unlock

beacon-chain/state/getters.go

@@ -451,7 +451,7 @@ func (b *BeaconState) ValidatorAtIndexReadOnly(idx uint64) (*ReadOnlyValidator,
 // ValidatorIndexByPubkey returns a given validator by its 48-byte public key.
 func (b *BeaconState) ValidatorIndexByPubkey(key [48]byte) (uint64, bool) {
 	b.lock.RLock()
-	b.lock.RUnlock()
+	defer b.lock.RUnlock()
 	idx, ok := b.valIdxMap[key]
 	return idx, ok
 }