Fix PyPy compilation #167

Job	Run time
Tests with external liberfa	37s
[ ubuntu-latest ]	1m 21s
[ macos-latest ]	1m 56s
[ windows-latest ]	2m 33s
Test with oldest supported versions of our dependencies [ ubuntu-20.04 ]	1m 8s
Test with medium old supported versions of our dependencies [ ubuntu-22.04 ]	1m 19s
build_and_publish / Load build targets	6s
Test with development versions of our dependencies [ ubuntu-latest ]	1m 34s
build_and_publish / Build source distribution	1m 18s
Code style checks [ ubuntu-latest ]	15s
Documentation build [ ubuntu-latest ]	1m 27s
build_and_publish / Build cp3*-manylinux_x86_64 wheels	2m 45s
build_and_publish / Build cp3*-musllinux_x86_64 wheels	2m 3s
build_and_publish / Build cp3*-manylinux_aarch64 wheels	3m 47s
build_and_publish / Build pp39-manylinux_x86_64 wheels	1m 48s
build_and_publish / Build pp39-manylinux_aarch64 wheels	3m 41s
build_and_publish / Build cp3*macosx_x86_64 wheels	3m 43s
build_and_publish / Build cp3*macosx_arm64 wheels	3m 38s
build_and_publish / Build pp39-macosx_x86_64 wheels	3m 14s
build_and_publish / Build pp39-macosx_arm64 wheels	40s
build_and_publish / Build cp3*win32 wheels	3m 25s
build_and_publish / Build cp3*win_amd64 wheels	3m 28s
build_and_publish / Build pp39-win_amd64 wheels	3m 33s
build_and_publish / Upload	1s
	49m 20s

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