threads: change main thread priority to 14 #679

Job	Run time
Build and package cores	11m 15s
Split off zephyr_main	10s
Split off zephyr_unoq	7s
Split off zephyr_contrib	7s
Split off zephyr	12s
Test zephyr_main:nano33ble	1m 57s
Test zephyr_main:portentah7	2m 37s
Test zephyr_main:giga	2m 31s
Test zephyr_main:portentac33	2m 35s
Test zephyr_main:opta	2m 32s
Test zephyr:unoq	2m 24s
Test zephyr_main:niclasense	2m 27s
Test zephyr_contrib:frdm_rw612	2m 23s
Test zephyr_contrib:ek_ra8d1	2m 19s
Test zephyr_contrib:frdm_mcxn947	2m 24s
verify-core	0s
Publish core	0s
Publish jsons	15s
Collect logs	10s
cleanup-artifacts	3s
	36m 28s

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