pico: prove empty block is flaky

[jsign]

Recently, I enabled Pico proving of Ethereum blocks since this is viable using ere.

In the PR that I did this, all worked fine, but when the PR was merged, the same identical run failed. I re-run two times and then passed. Today in an unrelated PR it failed, so I think there's some problem.

For now I'll disable it to avoid generating noise in all PRs.
Log of failure: https://github.com/eth-act/zkevm-benchmark-workload/actions/runs/18237274090/job/51933310942?pr=198

Reevaluate enabling again when Pico releases a new version.

[jsign]

For the same action, I could reproduce two runs:

• Attempt #1 succeeded
• Attempt #2 failed

Note this is for the same action/commit (i.e., attempt 2 is a "re-reun" from the first one), thus clearly proves the flakiness.
These runs also have more logs, but I don't see anything interesting.