ci: fix Dependabot config (#402) #642

Job	Run time
build (1.85.0, wasm32-unknown-unknown)	22s
build (1.85.0, thumbv7em-none-eabi)	19s
minimal-versions / minimal-versions	21s
build (stable, thumbv7em-none-eabi)	12s
build (stable, wasm32-unknown-unknown)	23s
test (1.85.0)	18s
test (stable)	20s
	2m 15s

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