relax swift-syntax version constraint to allow 603

Packages are updating to 603 and this can fail the dependency solver.

Author: diederich

Package.swift

@@ -40,7 +40,7 @@ let package = Package(
         .plugin(name: "BridgeJSCommandPlugin", targets: ["BridgeJSCommandPlugin"]),
     ],
     dependencies: [
-        .package(url: "https://github.com/swiftlang/swift-syntax", "600.0.0"..<"603.0.0")
+        .package(url: "https://github.com/swiftlang/swift-syntax", "600.0.0"..<"604.0.0")
     ],
     targets: [
         .target(