Devtools: Fix snapshotting of testnet_experiment_tools

Context

During the recent snapshot of the Oxford (v2) protocol, the newly-created 018 version of the Testnet experiment tools were copied from the Alpha version without updating the version of the protocol used. This MR fixes this small mistake.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR