p2p/test: prevent double close of pipes in test using fork processes

Context

The tests below are failing with bad file descriptor exception in the CI:

• p2p socket self connection message (https://gitlab.com/tezos/tezos/-/jobs/4461497139),
• p2p socket self peer id (https://gitlab.com/tezos/tezos/-/jobs/4460455242) and
• p2p socket nack (https://gitlab.com/tezos/tezos/-/jobs/4460198280)

These tests fork some processes from Process.detach.

In this function, some pipes are closed from the usage of close-on-exec flag and from explicit calls of close function in the child processes.

This MR use the patch made by @romain.nl that removes the usage of close-on-exec flag.

Fix #5868 (closed)

Manually testing the MR

Checklist

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