Use the worker loading from `src` directory

I think what we should do is
- open a issue on vitest repo to get this resolved (if it doesn't exist already)
- create an issue on lodestar repository, we also should make sure to reference all lines that have this in the issue
https://github.com/ChainSafe/lodestar/blob/d3005bf58efb527d2887a922689d74e32358bf79/packages/beacon-node/src/chain/bls/multithread/index.ts#L33
https://github.com/ChainSafe/lodestar/blob/d3005bf58efb527d2887a922689d74e32358bf79/packages/beacon-node/src/network/core/networkCoreWorkerHandler.ts#L33

_Originally posted by @nflaig in https://github.com/ChainSafe/lodestar/pull/6192#discussion_r1431236619_

Review the linked discussion and the worker-loading references in packages/beacon-node/src/chain/bls/multithread/index.ts and packages/beacon-node/src/network/core/networkCoreWorkerHandler.ts. First check whether a corresponding Vitest issue already exists. Done means the relevant Vitest and Lodestar issues are identified or created with all affected lines referenced.

Written by the indexing model from the issue text.