subsys:mgmt:mcumgr: Fix mcumgr assertion error #152849

Job	Run time
twister-build-prep / prep_pr	2m 55s
twister-build-prep / prep_push	0s
twister-build (1)	32m 10s
twister-build (2)	30m 23s
twister-build (3)	26m 5s
twister-build (4)	40m 9s
twister-build (5)	27m 41s
twister-build (6)	25m 47s
twister-build (7)	31m 28s
Publish Unit Tests Results	12s
Check Twister Status / all jobs passed	1s
	3h 36m 51s

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