Fix `Process::Status` for unknown signals #13037

Job	Run time
check_format	1m 35s
x86_64-gnu-test (1.7.3)	33m 35s
x86_64-gnu-test-preview_mt	5m 40s
x86_64-gnu-test (1.8.2)	34m 18s
x86_64-musl-test	37m 19s
x86_64-gnu-test (1.9.2)	36m 9s
x86_64-gnu-test (1.10.1)	34m 8s
x86_64-gnu-test (1.11.2)	35m 46s
x86_64-gnu-test (1.12.2)	35m 31s
x86_64-gnu-test (1.13.3)	32m 43s
x86_64-gnu-test (1.14.0)	36m 38s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	31m 55s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	33m 34s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	34m 32s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	35m 2s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	32m 46s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	32m 5s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	33m 49s
	9h 17m 5s

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