Fix tests without num-bigint feature #712

Job	Run time
bench	1m 24s
build pgo-optimized on ${{ matrix.os }} / ${{ matrix.interpreter }}	0s
build sdist	26s
build on ${{ matrix.os }} (${{ matrix.target }} - ${{ matrix.interpreter \|\| 'all' }}${{ (((matrix.os == 'linux') && format(' - {0}', (((matrix.manylinux == 'auto') && 'manylinux') \|\| matrix.manylinux))) \|\| '') }})	0s
fuzz skip	6m 17s
fuzz on ubuntu	6m 22s
lint	49s
resolve	10s
fuzz on macos	6m 10s
test jiter-python	49s
test build on ${{ matrix.target }}-${{ matrix.distro }}	0s
test build on ${{ matrix.os }}	0s
test rust-stable on ubuntu	39s
test rust-stable on macos	34s
test rust-1.75 on ubuntu	45s
test rust-nightly on ubuntu	1m 33s
inspect-pypi-assets	0s
check	2s
release	0s
release-python	0s
	26m 0s

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