op-e2e: Change final TestConfirmationDepth check

[trianglesphere]

Description

TestConfirmationDepth was consistently failing on the HTTP versions of the op-e2e test. It was failing at the last line that checked the verifier head block timestamp against the L1 head timestamp. I have changed it to compare the verifier L1 Origin number against the L1 head number.
Tests

Ran several times in CI & this seems less flaky.

Metadata

• Fixes ENG-3013

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Latest commit: 911b088

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[mslipper]

Going to merge this in an effort to reduce CI failures.