serdect: bump `toml` to v0.8 #891

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	4m 51s
test (1.65.0)	5m 15s
build (1.65.0, wasm32-unknown-unknown)	5m 44s
test (stable)	46s
build (stable, thumbv7em-none-eabi)	17s
build (stable, wasm32-unknown-unknown)	12s
minimal-versions / minimal-versions	1m 14s
	18m 19s

Provide feedback