Update Rust crate syn to v2.0.64

[oxide-renovate]

This PR contains the following updates:

Package	Type	Update	Change
syn	workspace.dependencies	patch	2.0.63 -> 2.0.64

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Release Notes

dtolnay/syn (syn)

v2.0.64

Compare Source

• 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)

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