fix custom signal handling, which was broken after #166 #20

Job	Run time
cygwin (python-3, 9)	4m 21s
CI (macos-13 with Python 3.10)	1m 12s
CI (macos-13 with Python 3.11)	1m 20s
CI (macos-13 with Python 3.12)	1m 10s
CI (macos-13 with Python 3.13-dev)	1m 53s
CI (macos-latest with Python 3.10)	1m 14s
CI (macos-latest with Python 3.11)	1m 0s
CI (macos-latest with Python 3.12)	1m 4s
CI (macos-latest with Python 3.13-dev)	1m 1s
CI (ubuntu-latest with Python 3.10)	59s
CI (ubuntu-latest with Python 3.11)	57s
CI (ubuntu-latest with Python 3.12)	54s
CI (ubuntu-latest with Python 3.13-dev)	1m 2s
CI (windows-latest with Python 3.10)	1m 37s
CI (windows-latest with Python 3.11)	1m 35s
CI (windows-latest with Python 3.12)	1m 36s
CI (windows-latest with Python 3.13-dev)	1m 53s
	24m 48s

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