Tezt: reduce memory consumption of p2p-swap-disable test by 2

This simple MR aims to reduce the memory consumption of the p2p-swap-disable test by 2, from ~7Gb+ to ~4Gb. It will reduce the pressure on the CI, speed up some tests and avoid flakiness.

Manually testing the MR

Run the test locally dune exec tezt/tests/main.exe -- --title 'p2p-swap-disable' --verbose and watch your ram usage.

Green CI.

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