Update Rust crate syn to v2.0.91 #697

Job	Run time
sdist	9m 25s
macos-x86_64	8m 43s
linux (x86_64-unknown-linux-gnu)	7m 34s
linux-arm (aarch64-unknown-linux-gnu, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	10m 47s
linux (i686-unknown-linux-gnu)	10m 29s
linux-arm (armv7-unknown-linux-gnueabihf, armv7)	10m 23s
macos-aarch64	12m 4s
linux-arm (arm-unknown-linux-musleabihf, arm)	10m 13s
windows (x86_64-pc-windows-msvc, x64)	15m 21s
windows (i686-pc-windows-msvc, x86)	15m 39s
linux-powerpc (powerpc64le-unknown-linux-gnu, ppc64le, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	11m 5s
linux-powerpc (powerpc64-unknown-linux-gnu, ppc64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	10m 49s
linux-s390x (s390x-unknown-linux-gnu, s390x)	14m 41s
musllinux (x86_64-unknown-linux-musl)	10m 20s
musllinux (i686-unknown-linux-musl)	9m 32s
musllinux-cross (aarch64-unknown-linux-musl, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	11m 1s
musllinux-cross (armv7-unknown-linux-musleabihf, armv7)	10m 9s
	3h 8m 15s

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