fix: always accept transactions with current nonce

[klkvr]

Closes #11922

Adds a check to ensure_valid which ensures we don't reject transactions which have on-chain nonce

[mattsse]

cool, can we add one test case for this:

insert nonce max slots nonce gapped txs
ensure further nonce gapped tx is rejected
ensure next nonce tx is accepted

[klkvr]

@mattsse I've modified existing test, lmk if a new one would be better