gh-116622: Switch test_stress_delivery_simultaneous from SIGUSR1 to SIGUSR2

[mhsmith]

On Android, test_stress_delivery_simultaneous was failing intermittently:

  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/test/test_signal.py", line 1340, in test_stress_delivery_simultaneous
    for _ in support.sleeping_retry(support.SHORT_TIMEOUT):
             ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/test/support/__init__.py", line 2509, in sleeping_retry
    for _ in busy_retry(timeout, err_msg, error=error):
             ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/test/support/__init__.py", line 2479, in busy_retry
    raise AssertionError(msg)
AssertionError: timeout (30.4 seconds)

When it fails, it also produces this log message:

Thread[6,tid=29634,WaitingInMainSignalCatcherLoop,Thread*=0xb400007e782136f0,peer=0x12cc0578,"Signal Catcher"]: reacting to signal 10

The root cause was the same as #116423 – SIGUSR1 being consumed by a pre-existing thread that we have no control over. I looked into killing that thread, but I couldn't find a safe way of doing it (#123982). So the simplest solution is to use a different signal instead.

It looks like this problem only happens when two different signals are sent so close together that one signal arrives while the other signal's C-level handler is still running. The other tests that use SIGUSR1 don't do this, so they don't need to be changed.

• Issue: Add support for Android as a target platform #116622

[freakboy3742]

!buildbot iOS

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @freakboy3742 for commit 07175ad 🤖

The command will test the builders whose names match following regular expression: iOS

The builders matched are:

• iOS ARM64 Simulator PR

[miss-islington-app]

Thanks @mhsmith for the PR, and @freakboy3742 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-123988 is a backport of this pull request to the 3.13 branch.