regrtest: Only report a leak if all test runs leak at least one file descriptor

Example on a recent buildbot run on AMD64 CentOS9 NoGIL Refleaks 3.x: https://buildbot.python.org/#/builders/1610/builds/4004

test_free_threading leaked [0, 1, 0] references, sum=1 (this is fine)
test_free_threading leaked [0, 1, -1] file descriptors, sum=0

For references, regrtest considers that a test leaks only if all test runs leak at least 1 reference.

For file descriptors, regrtest considers that a test leaks if at least one test run leaks a file descriptor.

In this example, leaked [0, 1, -1] file descriptors, sum=0 says that a test run creates a file descriptor without closing it (first run test, after the warmup): delta +1, but the following test run closes the file descriptor: delta -1. The sum=0 says that there is no leak at the end, all created file descriptors have been closed.

I propose to change the leak detection to only consider that there is a leak if all test runs leak at least one file descriptors.

Linked PRs

• gh-157629
• gh-157753

Inizia individuando il rilevamento delle perdite di descrittori di file di regrtest e verifica le PR collegate gh-157629 e gh-157753 per il lavoro già in corso. Usa l'esempio di buildbot come caso di riproduzione; il lavoro è completo quando una perdita viene segnalata solo se ogni esecuzione del test perde almeno un descrittore di file.