Update branch to release/5.9-20230510 for swift-syntax

Author: shahmishal

utils/update_checkout/update-checkout-config.json

@@ -240,7 +240,7 @@
                 "swift-asn1": "0.7.0",
                 "swift-driver": "release/5.9",
                 "swift-numerics": "1.0.1",
-                "swift-syntax": "release/5.9",
+                "swift-syntax": "release/5.9-20230510",
                 "swift-system": "1.1.1",
                 "swift-stress-tester": "release/5.9",
                 "swift-corelibs-xctest": "release/5.9",