tests

Don't duplicate CFLAGS #1274

Job	Run time
ci_setuptools (3.10, ubuntu-latest)	3m 52s
test (3.9, ubuntu-latest)	46s
collateral (diffcov)	48s
test (3.9, macos-latest)	1m 9s
test_cygwin (39, windows-latest)	5m 14s
collateral (docs)	32s
test (3.9, windows-latest)	2m 1s
test_msvc_python_mingw	2m 9s
test (3.13, ubuntu-latest)	56s
test_msys2_mingw (mingw64, x86_64, gcc, g++)	1m 46s
test (3.13, macos-latest)	56s
test_msys2_mingw (mingw32, i686, gcc, g++)	2m 4s
test (3.13, windows-latest)	3m 2s
test_msys2_mingw (ucrt64, ucrt-x86_64, gcc, g++)	2m 0s
test (3.10, ubuntu-latest)	42s
test_msys2_mingw (clang64, clang-x86_64, clang, clang++)	1m 40s
test (3.11, ubuntu-latest)	56s
test (3.12, ubuntu-latest)	45s
test (3.14, ubuntu-latest)	1m 17s
test (pypy3.10, ubuntu-latest)	1m 33s
check	4s
release	0s
	34m 12s

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