Update MSRV to 1.69.0 and update flake #72

Job	Run time
(Windows) Builds (x86_64-pc-windows-msvc)	55s
(OS X) Builds (aarch64-apple-ios)	2m 12s
(OS X) Builds (x86_64-apple-darwin)	2m 39s
(Linux) Builds (aarch64-linux-android)	2m 46s
Bench Compile (stable)	1m 48s
(Linux) Builds (x86_64-unknown-linux-musl)	2m 1s
Check (stable)	21s
(Linux) Builds (wasm32-unknown-unknown)	1m 50s
Check (beta)	25s
Rustfmt (nightly)	17s
Check (1.69.0)	3m 28s
Test Suite (stable)	1m 50s
Test Suite (1.69.0)	5m 17s
	25m 49s

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