Raise MSRV to 1.63 #301

Job	Run time
Bitrot check	1m 35s
Check no-std target thumbv6m-none-eabi	1m 35s
Test on ubuntu-latest with --all-features	1m 29s
Check no-std target wasm32-unknown-unknown	1m 39s
Test on i686-unknown-linux-gnu with --all-features	1m 39s
Test on ubuntu-latest with --no-default-features	1m 33s
Check no-std target wasm32-wasi	1m 39s
Test on i686-unknown-linux-gnu with --no-default-features	1m 40s
Test on windows-latest with --all-features	2m 52s
Test on windows-latest with --no-default-features	3m 2s
Book tests	1m 41s
Code coverage	2m 6s
Test on macOS-latest with --all-features	1m 24s
Test on macOS-latest with --no-default-features	1m 33s
Intra-doc links	1m 38s
Rustfmt	15s
	27m 20s

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