Bump defmt from 0.3.6 to 0.3.7 in /examples/stm32f4-event-printer #83

Job	Run time
stm32f4-event-printer	2m 11s
lib (1.62.0, use_alloc)	3m 38s
lib (1.62.0, use_alloc,defmt)	3m 28s
lib (1.62.0, use_heapless)	3m 35s
lib (1.62.0, use_heapless,defmt)	3m 34s
lib (stable, use_alloc)	1m 39s
lib (stable, use_alloc,defmt)	1m 42s
lib (stable, use_heapless)	1m 45s
lib (stable, use_heapless,defmt)	1m 47s
	23m 19s

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