Fix WinError 87 not handled in convert_oserror() (#2519)

[omprakash2929]

Summary

Fixes #2519

Process.send_signal(CTRL_C_EVENT/CTRL_BREAK_EVENT) on Windows can
raise a raw OSError (WinError 87, "the parameter is incorrect")
instead of NoSuchProcess, when the target process terminates on its
own right before the signal is sent (race condition).

Root cause

convert_oserror() in _pswindows.py only converts ProcessLookupError
and permission errors into psutil-friendly exceptions. WinError 87
raised by os.kill() in this race condition wasn't handled, so it
leaked out as a raw OSError.

Fix

Added a check for winerror == 87 in convert_oserror(), converting
it into NoSuchProcess, consistent with how other "process
disappeared" cases are already handled.

Testing

• tests/test_windows.py::TestProcess::test_ctrl_signals = PASSED
• tests/test_windows.py::TestProcess::test_send_signal = PASSED
• Attempted to reproduce the exact race condition locally with a
  stress test script; the underlying scenario is timing-dependent
  (as noted by the original reporter), so the fix targets the error
  code specifically, matching the documented WinError 87 behavior.

[omprakash2929]

@giampaolo This PR addresses the WinError 87 issue reported in #2519.

Since the race condition is timing-dependent and hard to reproduce
deterministically in a local test, I focused on making the fix logically
correct based on the documented error (WinError 87 - invalid parameter
raised by os.kill() when the process disappears right before the signal
is sent), and verified it doesn't break the existing signal-related tests:

• tests/test_windows.py::TestProcess::test_ctrl_signals = PASSED
• tests/test_windows.py::TestProcess::test_send_signal = PASSED

Happy to adjust the approach if you'd prefer a different way to handle this.