Update CI

Author: adam-fowler

.devcontainer/docker-compose.yml

@@ -3,7 +3,7 @@ version: "3.3"
 
 services:
   app:
-    image: swift:5.9
+    image: swift:6.0
     volumes:
       - ..:/workspace
       - mosquitto-socket:/workspace/mosquitto/socket

.github/workflows/ci.yml

@@ -50,11 +50,10 @@ jobs:
     strategy:
       matrix:
         tag:
-          - swift:5.7
-          - swift:5.8
           - swift:5.9
           - swift:5.10
           - swift:6.0
+          - swiftlang/swift:nightly-6.1-jammy
     container:
       image: ${{ matrix.tag }}
     services: