ICU-23246 Reduce default permissions and sign all release artifacts #4868

Job	Run time
clang-valgrind-test	10m 19s
clang-valgrind-intltest (utility)	7m 17s
clang-valgrind-intltest (regex)	7m 9s
clang-valgrind-intltest (idna)	5m 41s
clang-valgrind-intltest (icuserv)	5m 40s
clang-valgrind-intltest (rbnfp)	5m 50s
clang-valgrind-intltest (convert)	7m 0s
clang-valgrind-intltest (csdet)	5m 49s
clang-valgrind-intltest (rbnfrt)	6m 25s
clang-valgrind-intltest (translit)	6m 11s
clang-valgrind-intltest (format)	18m 3s
clang-valgrind-intltest (rbnf)	6m 46s
clang-valgrind-intltest (bidi)	5m 34s
clang-valgrind-intltest (spoof)	5m 14s
clang-valgrind-intltest (normalize)	6m 12s
clang-valgrind-intltest (collator)	6m 5s
clang-valgrind-intltest (rbbi)	9m 37s
	2h 4m 52s

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