Update swift-syntax dependency range

Author: andrewheard

Package.swift

@@ -177,7 +177,7 @@ let package = Package(
     ),
     .package(url: "https://github.com/google/app-check.git",
              "11.0.1" ..< "12.0.0"),
-    .package(url: "https://github.com/swiftlang/swift-syntax.git", "600.0.0" ..< "601.0.0"),
+    .package(url: "https://github.com/swiftlang/swift-syntax.git", "600.0.0" ..< "603.0.0"),
   ],
   targets: [
     .target(