[Core/Ref] Multiclass NMS: Fix vector initialization #34292

Job	Run time
Smart_CI	21s
Docker	54s
Build / Build	7m 44s
Debian Packages	0s
PyTorch Models tests	0s
OpenVINO JS API / OpenVINO JS API	1m 41s
CPU functional tests / CPU functional tests	4m 57s
C++ unit tests / C++ unit tests	13m 25s
ONNX Runtime Integration / ONNX Runtime Integration	4m 2s
Python unit tests / Python unit tests	8m 1s
OpenVINO tokenizers extension / OpenVINO tokenizers extension	1m 52s
Pytorch Layer Tests / PyTorch Layer Tests	2m 55s
Samples / Samples	6m 20s
TensorFlow Models tests	0s
TensorFlow Layer Tests / TensorFlow Layer Tests	3m 1s
ci/gha_overall_status_linux_arm64	1s
	55m 14s

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