Update syn requirement from 1.0.16 to 2.0.47

[dependabot[bot]]

Updates the requirements on syn to permit the latest version.

Release notes

Sourced from syn's releases.

2.0.47

• Improve error messages related to proc_macro::LexError (#1575)

Commits

• 2c96972 Release 2.0.47
• 845e295 Pull in proc-macro2 LexError fix
• 36e50fa Merge pull request #1575 from dtolnay/lexerror
• 7b3286a Preserve LexError's Display representation in syn::Error
• 1650c86 Release 2.0.46
• 65c7710 Pull in proc-macro2 sccache fix
• 61dee89 Merge pull request #1574 from dtolnay/precedence
• 36182d4 Move expression Precedence enum to own module
• 6bfa278 Release 2.0.45
• 3ba270b Merge pull request #1573 from dtolnay/pattype
• Additional commits viewable in compare view

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