OP tests: test 43 character nonce

Following up from this ticket:

#1217 (closed)

We have an RP test that warns if the nonce used is longer than 43 characters.

We hence should also have an OP test that tries a 43 character nonce and expects it to succeed. This doesn't need a new test module, it can be added into the second client happy flow test probably, it just needs requested_nonce_length to be set.

This should be done for OIDCC, FAPI1 & FAPI2, to match what was done for the RP tests in !1345 (merged)