unoq: restore main thread priority to 5 #756

Job	Run time
Build and package cores	10m 2s
Split off zephyr_contrib	16s
Split off zephyr	21s
Split off zephyr_main	8s
Split off zephyr_unoq	13s
Test zephyr_main:giga	2m 0s
Test zephyr_main:nano33ble	2m 31s
Test zephyr:unoq	2m 22s
Test zephyr_main:portentah7	2m 29s
Test zephyr_main:niclasense	2m 30s
Test zephyr_main:portentac33	2m 33s
Test zephyr_main:opta	2m 29s
Test zephyr_contrib:ek_ra8d1	2m 25s
Test zephyr_contrib:frdm_mcxn947	2m 32s
Test zephyr_contrib:frdm_rw612	2m 24s
Publish core	-1s
verify-core	0s
Collect logs	11s
Publish jsons	16s
cleanup-artifacts	4s
	35m 45s

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