Invalid gindex calculation

**Describe the bug**

```ts
import {ssz} from "@lodestar/types";

const {BeaconState} = ssz.phase0;
console.log(
  BeaconState.getPathInfo(["validators", 0, "activationEpoch"]).gindex === BeaconState.getPathInfo(["validators", 0, "pubkey"]).gindex
);
// true
```

**Expected behavior**

`false`
