Pin macOS script toolchain commands #199

Job	Run time
Miri	15m 31s
Platform tests (windows-latest)	1m 46s
Platform tests (macos-15-intel)	1m 10s
Platform tests (macos-latest)	31s
no_std target build (wasm32-unknown-unknown)	19s
Platform tests (macos-26)	23s
no_std target build (thumbv7em-none-eabihf)	18s
Platform tests (macos-15)	26s
Platform tests (ubuntu-latest)	28s
Format, lint, test, and audit	1m 9s
no_std target build (x86_64-unknown-freebsd)	21s
no_std target build (x86_64-unknown-linux-gnu)	15s
no_std target build (aarch64-unknown-linux-gnu)	21s
	22m 58s

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