Make tests pass when char is unsigned #9644

Job	Run time
check-ubuntu-20_04-make-clang	24m 32s
check-ubuntu-20_04-make-gcc	16m 18s
check-macos-11-make-clang	39m 10s
check-macos-12-cmake-clang	51m 32s
check-ubuntu-20_04-cmake-gcc	22m 26s
check-ubuntu-20_04-cmake-gcc-KNOWNBUG	2m 34s
check-ubuntu-20_04-cmake-gcc-THOROUGH	8m 4s
check-ubuntu-20_04-make-clang-smt-z3	3m 29s
check-ubuntu-22_04-cmake-gcc	20m 29s
check-ubuntu-22_04-cmake-gcc-13	18m 52s
check-ubuntu-22_04-cmake-gcc-32bit	19m 19s
check-ubuntu-22_04-make-clang	19m 22s
check-vs-2019-cmake-build-and-test	50m 13s
check-docker-image	20m 16s
check-string-table	2m 33s
check-vs-2022-make-build-and-test	49m 38s
codecov-coverage-report	27m 42s
include-what-you-use	26m 35s
windows-msi-package	5m 23s
	7h 8m 27s

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