ICU-21172 fix install race #2894

Job	Run time
clang-valgrind-test	9m 59s
clang-valgrind-intltest (utility)	7m 9s
clang-valgrind-intltest (normalize)	6m 52s
clang-valgrind-intltest (collator)	5m 36s
clang-valgrind-intltest (regex)	5m 36s
clang-valgrind-intltest (format)	16m 9s
clang-valgrind-intltest (translit)	6m 2s
clang-valgrind-intltest (rbbi)	8m 13s
clang-valgrind-intltest (rbnf)	6m 29s
clang-valgrind-intltest (rbnfrt)	6m 8s
clang-valgrind-intltest (icuserv)	5m 9s
clang-valgrind-intltest (idna)	5m 30s
clang-valgrind-intltest (convert)	6m 37s
clang-valgrind-intltest (rbnfp)	5m 17s
clang-valgrind-intltest (csdet)	5m 27s
clang-valgrind-intltest (spoof)	5m 18s
clang-valgrind-intltest (bidi)	5m 48s
	1h 57m 19s

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