Fix use after scope error active_transactions.vacancy test

[thsfs]

Error got when running ASAN test on core_test.

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==core_test==255418==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fff63ab5320 at pc 0x5626fe4da09e bp 0x7fff63ab4260 sp 0x7fff63ab4258
WRITE of size 1 at 0x7fff63ab5320 thread T0
    #0 0x5626fe4da09d in std::__atomic_base<bool>::store(bool, std::memory_order) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/atomic_base.h:457:2
    #1 0x5626fe4da09d in std::__atomic_base<bool>::operator=(bool) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/atomic_base.h:349:2
    #2 0x5626fe4ba1a9 in std::atomic<bool>::operator=(bool) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/atomic:80:22
    #3 0x5626fe4aa412 in active_transactions_vacancy_Test::TestBody()::$_4::operator()() const /home/***/nano-node/nano/core_test/active_transactions.cpp:1305:55