Fix tests for x448/x25519 #946

Job	Run time
mypy	14s
build_python_27 (ubuntu-20.04, yes)	2m 36s
build_python_27 (ubuntu-20.04, no)	2m 29s
python_no_gil	2m 46s
build (3.6, yes, ubuntu-20.04)	2m 42s
build_python_27 (windows-latest, yes)	3m 28s
test_c_linux (0, x64)	50s
build_python_27 (windows-latest, no)	4m 31s
build (3.6, no, ubuntu-20.04)	2m 32s
test_c_linux (0, x32)	1m 1s
test_c_windows (x64)	44s
build (3.7, yes, ubuntu-20.04)	2m 26s
test_c_linux (1, x64)	55s
test_c_windows (win32)	48s
build (3.7, no, ubuntu-20.04)	2m 20s
test_c_linux (1, x32)	1m 10s
build (3.8, yes, ubuntu-20.04)	2m 19s
build (3.8, no, ubuntu-20.04)	2m 23s
build (3.9, yes, ubuntu-20.04)	2m 17s
build (3.9, no, ubuntu-20.04)	2m 21s
build (3.10, yes, ubuntu-20.04)	2m 22s
build (3.10, no, ubuntu-20.04)	2m 10s
build (3.11, yes, ubuntu-20.04)	2m 0s
build (3.11, no, ubuntu-20.04)	1m 51s
build (3.12, yes, ubuntu-20.04)	1m 59s
build (3.12, no, ubuntu-20.04)	2m 4s
build (3.13-dev, yes, ubuntu-20.04)	2m 0s
build (3.13-dev, no, ubuntu-20.04)	2m 11s
build (3.12, yes, macos-12)	3m 29s
build (3.12, no, windows-latest)	4m 2s
build (3.12, yes, windows-latest)	4m 3s
build (pypy2.7, no, ubuntu-latest)	1m 33s
build (pypy3.9, no, ubuntu-latest)	1m 39s
	1h 12m 15s

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