[3.11] gh-71052: Use `raise_signal` in `ThreadSignals.test_signals` (GH-116423) (#116617)

gh-71052: Use `raise_signal` in `ThreadSignals.test_signals` (GH-116423)

Use `raise_signal` rather than `kill` in `ThreadSignals.test_signals`
(cherry picked from commit 34920f36917de0d4e658cf94992d53a5a7f27f51)

Co-authored-by: Malcolm Smith <smith@chaquo.com>