Bump general MSRV to 1.63 #2974

Job	Run time
cargo clippy	14s
cargo bench	53s
cargo +stable build	31s
cargo +1.36 build (futures-{core, io, sink})	50s
cargo +beta build	37s
cargo doc	19s
cargo +nightly build	34s
cargo hack check --feature-powerset	2m 19s
cargo fmt	5s
cargo miri test	15m 4s
cargo minimal-versions build	24s
cargo test -Z sanitizer=address	3m 29s
cargo build --target thumbv7m-none-eabi	27s
cargo test -Z sanitizer=memory	5m 28s
cargo build --target thumbv6m-none-eabi	26s
cargo test (ubuntu-latest)	2m 47s
cargo test -Z sanitizer=thread	2m 37s
cargo +1.63 build	1m 8s
cargo test (macos-latest)	6m 11s
cargo test (windows-latest)	4m 39s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	3m 42s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	6m 4s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	6m 22s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	3m 45s
	1h 8m 55s

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