fix chunk fetching network compatibility zombienet test (#6988)

Fix this zombienet test

It was failing because in
https://github.com/paritytech/polkadot-sdk/pull/6452 I enabled the v2
receipts for testnet genesis,
so the collators started sending v2 receipts with zeroed collator
signatures to old validators that were still checking those signatures
(which lead to disputes, since new validators considered the candidates
valid).

The fix is to also use an old image for collators, so that we don't
create v2 receipts.

We cannot remove this test yet because collators also perform chunk
recovery, so until all collators are upgraded, we need to maintain this
compatibility with the old protocol version (which is also why
systematic recovery was not yet enabled)