ci: fix swift 6 docker img ref

Author: alephao

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
     timeout-minutes: 5
     strategy:
       matrix:
-        image: ["swift:5.8", "swift:5.9", "swift:5.10", "swiftlang/swift:6.0-jammy"]
+        image: ["swift:5.8", "swift:5.9", "swift:5.10", "swift:6.0-jammy"]
 
     container:
       image: ${{ matrix.image }}