Fix tests for x448/x25519 #947

Job	Run time
mypy	13s
test_c_linux (0, x64)	53s
build_python_27 (ubuntu-20.04, yes)	2m 32s
test_c_linux (0, x32)	1m 0s
build_python_27 (ubuntu-20.04, no)	2m 27s
test_c_linux (1, x64)	54s
test_c_linux (1, x32)	1m 7s
build_python_27 (windows-latest, yes)	4m 32s
build_python_27 (windows-latest, no)	3m 57s
python_no_gil	3m 2s
build (3.6, yes, ubuntu-20.04)	2m 27s
test_c_windows (x64)	32s
build (3.6, no, ubuntu-20.04)	2m 24s
test_c_windows (win32)	1m 26s
build (3.7, yes, ubuntu-20.04)	2m 25s
build (3.7, no, ubuntu-20.04)	2m 24s
build (3.8, yes, ubuntu-20.04)	2m 16s
build (3.8, no, ubuntu-20.04)	2m 13s
build (3.9, yes, ubuntu-20.04)	2m 7s
build (3.9, no, ubuntu-20.04)	2m 17s
build (3.10, yes, ubuntu-20.04)	2m 8s
build (3.10, no, ubuntu-20.04)	2m 14s
build (3.11, yes, ubuntu-20.04)	1m 58s
build (3.11, no, ubuntu-20.04)	2m 2s
build (3.12, yes, ubuntu-20.04)	1m 57s
build (3.12, no, ubuntu-20.04)	2m 4s
build (3.13-dev, yes, ubuntu-20.04)	2m 2s
build (3.13-dev, no, ubuntu-20.04)	2m 13s
build (3.12, yes, macos-12)	3m 0s
build (3.12, no, windows-latest)	3m 33s
build (3.12, yes, windows-latest)	3m 40s
build (pypy2.7, no, ubuntu-latest)	1m 27s
build (pypy3.9, no, ubuntu-latest)	1m 37s
	1h 11m 3s

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