Bump proc_macro2 to support building on nightly rust #981

Job	Run time
Extract crate metadata	4s
Ensure 'cargo fmt' has been run	12s
Minimum supported rust version	2m 11s
aarch64-unknown-linux-gnu (ubuntu-20.04)	7m 8s
arm-unknown-linux-gnueabihf (ubuntu-20.04)	8m 54s
arm-unknown-linux-musleabihf (ubuntu-20.04)	5m 39s
i686-pc-windows-msvc (windows-2019)	6m 34s
i686-unknown-linux-gnu (ubuntu-20.04)	7m 31s
i686-unknown-linux-musl (ubuntu-20.04)	5m 1s
x86_64-apple-darwin (macos-12)	5m 55s
x86_64-pc-windows-gnu (windows-2019)	7m 24s
x86_64-pc-windows-msvc (windows-2019)	6m 18s
x86_64-unknown-linux-gnu (ubuntu-20.04)	6m 18s
x86_64-unknown-linux-musl (ubuntu-20.04)	7m 19s
Publish to Winget	0s
	1h 16m 28s

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