tools/check-commits.sh: allow AUTHORS as a prefix in commit message s… #18429

Job	Run time
dashboard	2m 9s
aux	4m 43s
build	4m 11s
arch (presubmit_arch_linux)	10m 37s
arch (presubmit_arch_netbsd)	3m 44s
arch (presubmit_arch_openbsd)	3m 51s
arch (presubmit_arch_windows)	3m 35s
arch (presubmit_arch_darwin)	3m 44s
arch (presubmit_arch_executor)	3m 18s
gvisor	3m 36s
race_dashboard	3m 17s
arch (presubmit_arch_freebsd)	6m 26s
race	7m 5s
old	7m 8s
	1h 7m 24s

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