serdect: bump `toml` to v0.8 #728

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	5m 49s
build (1.65.0, wasm32-unknown-unknown)	5m 47s
build (stable, thumbv7em-none-eabi)	25s
build (stable, wasm32-unknown-unknown)	36s
test (1.65.0)	6m 1s
test (stable)	39s
minimal-versions / minimal-versions	49s
	20m 6s

Provide feedback