generator: Use Swift 6.0.2 by default (#163)

Testing:
* EndToEndTests continue to pass locally, but cannot run in CI
* All other tests pass locally and in CI

Author: euanh

Sources/GeneratorCLI/GeneratorCLI.swift

@@ -98,7 +98,7 @@ extension GeneratorCLI {
     var swiftBranch: String? = nil
 
     @Option(help: "Version of Swift to supply in the bundle.")
-    var swiftVersion = "5.10.1-RELEASE"
+    var swiftVersion = "6.0.2-RELEASE"
 
     @Option(
       help: """