Update CI swift versions

Author: adam-fowler

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ on:
 
 jobs:
   macos:
-    runs-on: macOS-13
+    runs-on: macOS-14
     steps:
     - name: Checkout
       uses: actions/checkout@v4
@@ -36,10 +36,9 @@ jobs:
     strategy:
       matrix:
         tag:
-          - swift:5.8
           - swift:5.9
           - swift:5.10
-          - swiftlang/swift:nightly-6.0-jammy
+          - swift:6.0
     container:
       image: ${{ matrix.tag }}
     steps: