ci/package_core: fix multi-artifact core upload #642

Job	Run time
Build and package cores	8m 55s
Split off zephyr	14s
Split off zephyr_contrib	9s
Split off zephyr_main	17s
Split off zephyr_unoq	7s
Test zephyr_main:giga	2m 46s
Test zephyr_main:nano33ble	2m 45s
Test zephyr_main:niclasense	2m 39s
Test zephyr_main:opta	2m 47s
Test zephyr:unoq	2m 46s
Test zephyr_main:portentah7	2m 41s
Test zephyr_contrib:ek_ra8d1	2m 32s
Test zephyr_contrib:frdm_rw612	2m 44s
Test zephyr_contrib:frdm_mcxn947	2m 38s
Test zephyr_main:portentac33	2m 48s
Collect logs	10s
Publish core	28s
Publish jsons	16s
verify-core	0s
cleanup-artifacts	3s
	37m 45s

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