drivers: bluetooth: silabs: Improve robustness under load #157250

Job	Run time
twister-build-prep / prep_pr	3m 32s
twister-build-prep / prep_push	0s
twister-build (1)	47m 54s
twister-build (2)	46m 39s
twister-build (3)	33m 13s
twister-build (4)	1h 8m 33s
twister-build (5)	39m 17s
twister-build (6)	24m 34s
twister-build (7)	29m 23s
twister-build (8)	33m 5s
Publish Unit Tests Results	12s
Check Twister Status / all jobs passed	1s
	5h 26m 23s

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