Update MSRV to 1.60 from 1.56 #518

Job	Run time
cross_compile_aarch64 (1.60)	2m 42s
cross_compile_aarch64 (1.60, std)	2m 29s
build_test (i586-pc-windows-msvc, 1.60, windows-latest)	3m 10s
cross_compile_aarch64 (stable)	31s
build_test (i586-pc-windows-msvc, stable, windows-latest)	57s
cross_compile_aarch64 (stable, std)	33s
build_test (i586-pc-windows-msvc, beta, windows-latest)	1m 5s
cross_compile_aarch64 (nightly)	29s
build_test (i586-pc-windows-msvc, nightly, windows-latest)	57s
cross_compile_aarch64 (nightly, std)	33s
build_test (i686-pc-windows-msvc, 1.60, windows-latest)	3m 3s
build_test (i686-pc-windows-msvc, stable, windows-latest)	1m 11s
build_test (i686-pc-windows-msvc, beta, windows-latest)	1m 1s
build_test (i686-pc-windows-msvc, nightly, windows-latest)	1m 1s
build_test (x86_64-pc-windows-msvc, 1.60, windows-latest)	3m 4s
build_test (x86_64-pc-windows-msvc, stable, windows-latest)	1m 26s
build_test (x86_64-pc-windows-msvc, beta, windows-latest)	57s
build_test (x86_64-pc-windows-msvc, nightly, windows-latest)	54s
build_test (wasm32-wasi, 1.60, ubuntu-latest, v5.0.0)	2m 23s
build_test (wasm32-wasi, stable, ubuntu-latest, v5.0.0)	32s
build_test (wasm32-wasi, beta, ubuntu-latest, v5.0.0)	32s
build_test (wasm32-wasi, nightly, ubuntu-latest, v5.0.0)	32s
	30m 2s

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