Update MSRV to 1.81 #625

Job	Run time
format	15s
Clippy	49s
cargo-test (ubuntu-22.04, default, stable)	2m 6s
cargo-test (macos-13, default, stable)	3m 59s
cargo-build (aarch64-linux-android, ubuntu-22.04)	2m 40s
cargo-test (windows-2019, default, stable)	4m 37s
cargo-build (armv7-linux-androideabi, ubuntu-22.04)	2m 40s
cargo-test (ubuntu-22.04, beta)	2m 50s
cargo-test (ubuntu-22.04, blocking)	3m 8s
cargo-test (ubuntu-22.04, blocking,beta)	3m 43s
cargo-test (ubuntu-22.04, tls-rustls --no-default-features)	2m 25s
cargo-test (ubuntu-22.04, tls-vendored-openssl --no-default-features)	3m 53s
cargo-build (i686-linux-android, ubuntu-22.04)	2m 39s
cargo-test (ubuntu-22.04, beta, default)	2m 17s
cargo-build (x86_64-linux-android, ubuntu-22.04)	2m 40s
cargo-test (ubuntu-22.04, 1.81.0, default)	4m 55s
cargo-build (x86_64-unknown-linux-musl, ubuntu-22.04)	1m 30s
cargo-build (aarch64-apple-ios, macos-13)	2m 47s
	49m 53s

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