Update syn #740

Job	Run time
Docs (Detect cases where documentation links don't resolve and such)	22s
test (i686-pc-windows-msvc (stable), windows-2019, stable, i686-pc-windows-msvc, x86)	13m 15s
test (x86_64-pc-windows-msvc (stable), windows-2019, stable, x86_64-pc-windows-msvc, x64)	14m 8s
test (x86_64-pc-windows-msvc (beta), windows-2019, beta, x86_64-pc-windows-msvc, x64)	15m 31s
test (x86_64-unknown-linux-gnu (stable), ubuntu-20.04, stable, x86_64-unknown-linux-gnu)	7m 43s
test (x86_64-unknown-linux-gnu (beta), ubuntu-20.04, beta, x86_64-unknown-linux-gnu)	8m 18s
test (x86_64-apple-darwin (stable), macos-13, stable, x86_64-apple-darwin)	15m 26s
test (x86_64-apple-darwin (beta), macos-13, beta, x86_64-apple-darwin)	10m 57s
	1h 25m 40s

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