MerkleCheckTraceGenTest fails with assertion

[fcarreiro]

If you compile with clag20-assert, this test fails.

[ RUN      ] MerkleCheckTraceGenTest.MixedEvents
vm2_tests: /mnt/user-data/facundo/aztec-packages/barretenberg/cpp/src/barretenberg/vm2/tracegen/merkle_check_trace.cpp:114:
void bb::avm2::tracegen::MerkleCheckTraceBuilder::process(const simulation::EventEmitterInterface<simulation::MerkleCheckEvent>::Container &, TraceContainer &): Assertion `current_index_in_layer == 0' failed.