ICU-22830 Fix memLeak in numrange_fluent.cpp #2471

Job	Run time
clang-valgrind-test	7m 42s
clang-valgrind-intltest (utility)	4m 4s
clang-valgrind-intltest (normalize)	6m 27s
clang-valgrind-intltest (collator)	4m 58s
clang-valgrind-intltest (regex)	5m 14s
clang-valgrind-intltest (format)	7m 38s
clang-valgrind-intltest (translit)	5m 4s
clang-valgrind-intltest (rbbi)	7m 7s
clang-valgrind-intltest (rbnf)	5m 58s
clang-valgrind-intltest (rbnfrt)	5m 15s
clang-valgrind-intltest (icuserv)	4m 55s
clang-valgrind-intltest (idna)	5m 21s
clang-valgrind-intltest (convert)	6m 47s
clang-valgrind-intltest (rbnfp)	5m 8s
clang-valgrind-intltest (csdet)	5m 28s
clang-valgrind-intltest (spoof)	5m 5s
clang-valgrind-intltest (bidi)	5m 15s
	1h 37m 26s

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