Specify 1.67.1 as MSRV #175

Job	Run time
cross-linux (stable, aarch64, aarch64-unknown-linux-gnu, aarch64-linux-gnu)	47s
aarch64-apple-ios (stable)	33s
build (windows-2019, stable)	1m 53s
cross-linux (stable, arm, armv7-unknown-linux-gnueabihf, arm-linux-gnueabihf)	42s
aarch64-apple-ios (1.67)	3m 53s
build (windows-2019, 1.67)	4m 20s
cross-linux (stable, i386, i686-unknown-linux-gnu, i686-linux-gnu)	48s
android (stable, aarch64-linux-android)	16s
build (ubuntu-latest, stable)	19s
cross-linux (1.67, aarch64, aarch64-unknown-linux-gnu, aarch64-linux-gnu)	2m 45s
android (stable, armv7-linux-androideabi)	15s
cross-windows (stable, aarch64-pc-windows-msvc)	1m 52s
build (ubuntu-latest, 1.67)	2m 23s
cross-linux (1.67, arm, armv7-unknown-linux-gnueabihf, arm-linux-gnueabihf)	2m 43s
android (stable, x86_64-linux-android)	15s
cross-windows (stable, i686-pc-windows-msvc)	2m 7s
build (macos-latest, stable)	30s
cross-linux (1.67, i386, i686-unknown-linux-gnu, i686-linux-gnu)	2m 48s
android (stable, i686-linux-android)	16s
cross-windows (1.67, aarch64-pc-windows-msvc)	3m 44s
build (macos-latest, 1.67)	4m 5s
android (1.67, aarch64-linux-android)	2m 28s
cross-windows (1.67, i686-pc-windows-msvc)	3m 47s
android (1.67, armv7-linux-androideabi)	2m 30s
freebsd (14.0, stable)	6m 5s
android (1.67, x86_64-linux-android)	2m 26s
android (1.67, i686-linux-android)	2m 22s
freebsd (14.0, 1.67)	6m 1s
freebsd (13.2, stable)	6m 6s
freebsd (13.2, 1.67)	6m 8s
	1h 15m 7s

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