Bump syn from 2.0.61 to 2.0.64 in /contracts in the deps group across 1 directory

[dependabot]

Bumps the deps group with 1 update in the /contracts directory: syn.

Updates syn from 2.0.61 to 2.0.64

Release notes

Sourced from syn's releases.

2.0.64

• Support using ParseBuffer across catch_unwind (#1646)
• Validate that the expression in a let-else ends in brace as required by rustc (#1648, #1649)
• Legalize invalid const generic arguments by wrapping in braces (#1654, #1655)
• Fix some expression precedence edge cases involving break and return in loop headers (#1656)
• Always print closure bodies with a brace when the closure has an explicit return type (#1658)
• Automatically insert necessary parentheses in ToTokens for Expr when required by expression precedence (#1659)
• Support struct literal syntax in match guard expressions (#1662)

2.0.63

• Parse and print long if-else-if chains without reliance on deep recursion to avoid overflowing stack (#1644, #1645)

2.0.62

• Reject invalid unparenthesized range and comparison operator expressions (#1642, #1643)

Commits

• 98a62cb Release 2.0.64
• 1f8eddb Merge pull request #1662 from dtolnay/guardstruct
• 0a3d3bd Fix parsing of struct literal in match guard expression
• f464193 Merge pull request #1659 from dtolnay/needspar
• afa1c72 Add more auto-parenthesization tests
• 532d3a3 Insert necessary parentheses in ToTokens for Expr
• 1b6a450 Add test of parenthesis insertion by Expr's ToTokens
• 83ea289 Merge pull request #1658 from dtolnay/closurebrace
• 206d897 Create braces around closure body during printing if needed
• 9b60027 Ignore struct_excessive_bools pedantic clippy lint
• Additional commits viewable in compare view

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[dependabot]

Looks like syn is updatable in another way, so this is no longer needed.