Merge pull request #76052 from rintaro/6.0-swift-testing-scheme-6.0.0

[6.0][update-checkout] Add swift-testing to release/6.0.0 scheme

Author: rintaro

utils/update_checkout/update-checkout-config.json

@@ -234,6 +234,7 @@
                 "swift-syntax": "release/6.0.0",
                 "swift-system": "1.3.0",
                 "swift-stress-tester": "release/6.0.0",
+                "swift-testing": "release/6.0.0",
                 "swift-corelibs-xctest": "release/6.0.0",
                 "swift-corelibs-foundation": "release/6.0.0",
                 "swift-foundation": "release/6.0.0",