test_subprocess can timeout on systems with excessive max file descriptors

[itamaro]

Bug report

Bug description:

On some systems, os.sysconf("SC_OPEN_MAX") may return a very large value (i.e. 2**30), leading to the subprocess test timing out (or run forever).

CPython versions tested on:

CPython main branch, 3.14, 3.13, 3.12

Operating systems tested on:

Linux

Linked PRs

• gh-134954: Hard-cap max file descriptors in subprocess test fd_status #134955
• [3.14] gh-134954: Hard-cap max file descriptors in subprocess test fd_status (GH-134955) #134980
• [3.13] gh-134954: Hard-cap max file descriptors in subprocess test fd_status (GH-134955) #134981