threads: change main thread priority to 14 #651

Job	Run time
Build and package cores	9m 5s
Split off zephyr	11s
Split off zephyr_unoq	13s
Split off zephyr_main	8s
Split off zephyr_contrib	8s
Test zephyr_main:nano33ble	2m 30s
Test zephyr_main:giga	2m 38s
Test zephyr_main:niclasense	2m 30s
Test zephyr_contrib:frdm_mcxn947	2m 26s
Test zephyr:unoq	2m 24s
Test zephyr_main:opta	2m 33s
Test zephyr_main:portentah7	2m 30s
Test zephyr_contrib:ek_ra8d1	2m 26s
Test zephyr_contrib:frdm_rw612	2m 29s
Test zephyr_main:portentac33	2m 36s
Publish jsons	12s
Collect logs	7s
Publish core	0s
verify-core	0s
cleanup-artifacts	3s
	35m 9s

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