elliptic-curve: bump `serdect` to v0.3.0-rc.0 (#1670) #2872

Job	Run time
build (1.73.0, thumbv7em-none-eabi)	39s
build (1.73.0, wasm32-unknown-unknown)	40s
minimal-versions	0s
build (stable, thumbv7em-none-eabi)	37s
test (1.73.0)	30s
build (stable, wasm32-unknown-unknown)	34s
test (stable)	23s
test (nightly)	28s
	3m 51s

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