Bump swift-syntax to 602.0.0 and swift-macro-testing to match.

[willtemperley]

Checklist

• I've added at least one test that validates that my change is working, if appropriate
• I've followed the code style of the rest of the project
• I've run Scripts/format.sh to correctly format my change
• I've read the Contribution Guidelines
• I've updated the documentation if necessary