fix QtSLiM build error #1254

Job	Run time
canceller	4s
tests-Windows-CLI (mingw64, x86_64, 3.8)	15m 15s
tests-Windows-CLI (ucrt64, ucrt-x86_64, 3.8)	16m 4s
tests-Unix-CLI (ubuntu-20.04, 7, 3.8)	5m 57s
tests-Unix-CLI (ubuntu-20.04, 11, 3.9)	6m 20s
tests-Unix-GUI (ubuntu-20.04, 5.9.5, 7)	5m 13s
tests-Windows-GUI (mingw64, x86_64)	12m 10s
tests-Unix-CLI (macos-12, 3.8)	8m 32s
tests-Unix-GUI (ubuntu-20.04, 5.15.2, 11)	5m 48s
tests-Windows-GUI (ucrt64, ucrt-x86_64)	12m 33s
tests-windows-latest-pacman (mingw64, x86_64)	1m 51s
tests-Unix-GUI (ubuntu-22.04, 5.15.2, 12)	6m 51s
tests-Unix-CLI (macos-13, 3.9)	9m 59s
tests-windows-latest-pacman (ucrt64, ucrt-x86_64)	1m 48s
tests-Unix-GUI (ubuntu-22.04, 6.7.2, 12)	7m 6s
tests-Unix-GUI (macos-12, 5.9.5)	6m 29s
tests-Unix-GUI (macos-13, 5.15.2)	7m 20s
tests-Unix-GUI (macos-13, 6.7.2)	9m 36s
	2h 18m 56s

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