[3.12] gh-110033: Fix signal test_interprocess_signal() (GH-110035) (#110040)

gh-110033: Fix signal test_interprocess_signal() (GH-110035)

Fix test_interprocess_signal() of test_signal. Make sure that the
subprocess.Popen object is deleted before the test raising an
exception in a signal handler. Otherwise, Popen.__del__() can get the
exception which is logged as "Exception ignored in: ...." and the
test fails.
(cherry picked from commit 7e0fbf5175fcf21dae390ba68b7f49706d62aa49)

Co-authored-by: Victor Stinner <vstinner@python.org>