tests

`spawn`: don't force param `cmd` to be mutable #1482

Job	Run time
test_msvc_python_mingw	1m 31s
collateral (docs)	31s
ci_setuptools (3.10, ubuntu-latest)	1m 40s
collateral (diffcov)	59s
test_msys2_mingw (mingw32, i686, gcc, g++)	1m 31s
test_msys2_mingw (mingw64, x86_64, gcc, g++)	1m 32s
test_msys2_mingw (ucrt64, ucrt-x86_64, gcc, g++)	1m 28s
test_msys2_mingw (clang64, clang-x86_64, clang, clang++)	1m 35s
test_cygwin (39, windows-latest)	1m 28s
test (3.9, macos-latest)	1m 8s
test (3.13, ubuntu-latest)	59s
test (3.13, macos-latest)	55s
test (3.9, windows-latest)	1m 32s
test (3.9, ubuntu-latest)	44s
test (3.13, windows-latest)	1m 34s
test (3.14, ubuntu-latest)	1m 23s
test (pypy3.10, ubuntu-latest)	1m 40s
test (3.12, ubuntu-latest)	53s
test (3.11, ubuntu-latest)	53s
test (3.10, ubuntu-latest)	56s
check	2s
release	1s
	24m 55s

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