Update dependencies

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
proc-macro2	workspace.dependencies	patch	1.0.85 -> 1.0.86
syn	workspace.dependencies	patch	2.0.66 -> 2.0.68

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Release Notes

dtolnay/proc-macro2 (proc-macro2)

v1.0.86

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• Documentation improvements

dtolnay/syn (syn)

v2.0.68

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• Improve panic location when parse_quote! parses invalid syntax (#​1690, thanks @​stepancheg)
• More efficient peek implementation for Group and Lifetime (#​1687)

v2.0.67

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• Produce more accurate error message locations for errors located at the end of a nested group (#​1679, #​1680)
• Support peeking LitCStr in ParseStream::peek (#​1682)

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