chore: update Motoko version to 1.2.0 #6758

Job	Run time
build_dfx (x86_64-unknown-linux-gnu)	13m 24s
build_dfx (aarch64-apple-darwin)	13m 38s
build_dfx (x86_64-apple-darwin)	15m 14s
build_dfx (aarch64-unknown-linux-gnu)	10m 44s
publishable:required	2s
publish	0s
publish-assets	-1s
	53m 1s

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