Bump actions/checkout from 5 to 6 #11363

Job	Run time
check-ubuntu-24_04-make-clang-smt-z3	17m 34s
check-ubuntu-24_04-make-gcc	32m 30s
check-ubuntu-24_04-make-clang	34m 57s
check-ubuntu-24_04-cmake-gcc	30m 46s
check-ubuntu-24_04-cmake-gcc-KNOWNBUG	16m 48s
check-ubuntu-22_04-cmake-gcc-32bit	29m 44s
windows-msi-package	27m 58s
check-string-table	1m 43s
check-macos-15-intel-make-clang	1h 23m 5s
check-vs-2025-cmake-build-and-test	55m 21s
check-docker-image	21m 5s
check-ubuntu-22_04-cmake-gcc	29m 13s
check-ubuntu-22_04-make-clang	34m 23s
check-ubuntu-24_04-arm-cmake-gcc	22m 9s
check-ubuntu-24_04-cmake-gcc-THOROUGH	21m 57s
check-macos-14-cmake-clang	2h 39m 51s
check-vs-2022-make-build-and-test	1h 5m 34s
check-ubuntu-24_04-cmake-gcc-14	30m 19s
include-what-you-use	14m 55s
	12h 9m 52s

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