signature: bump `hex-literal` to v0.4 #2428

Job	Run time
doc	30s
build (1.65.0, thumbv7em-none-eabi)	6m 0s
build (1.65.0, wasm32-unknown-unknown)	4m 5s
minimal-versions	38s
build (stable, thumbv7em-none-eabi)	36s
test (1.65.0)	3m 50s
build (stable, wasm32-unknown-unknown)	46s
test (stable)	29s
test (nightly)	46s
	17m 40s

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