build(deps): update syn requirement from 2.0.119 to 3.0.3 in /test/cargo-fuzz

[dependabot]

Updates the requirements on syn to permit the latest version.

Release notes

Sourced from syn's releases.

3.0.3

• Documentation improvements

Commits

• 23dbaab Release 3.0.3
• 16aad4e Merge pull request #2071 from dtolnay/compatibility
• 42181b8 Add explanation of compatibility strategy
• f3af08e Update test suite to nightly-2026-07-21
• 88ee7be Release 3.0.2
• 587bc20 Merge pull request #2070 from dtolnay/emptyrange
• 96801f7 Allow Error::new_range at empty cursor range
• 9dc16c9 Merge pull request #2069 from dtolnay/prevspan
• 1db76b7 Align on using impl trait across all Error constructors
• bfa1ebf Make Cursor::prev_span public
• Additional commits viewable in compare view

[def-]

Closing: this PR comes from the /test/cargo-fuzz dependabot directory, which edits the root Cargo.toml without owning the root Cargo.lock, so it can never pass --locked. #38315 removes that directory. Bumps for these crates come from the / directory instead.

[dependabot]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version. You can also ignore all major, minor, or patch releases for a dependency by adding an ignore condition with the desired update_types to your config file.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.