Dev Containers: Update 'GHC 9.6 (recommended)'

- Update Stack to v3.1.1

.devcontainer/ghc-9.6/devcontainer.json

@@ -6,7 +6,7 @@
     "args": {
       "GHC_VERSION": "9.6",
       "HLS_VERSION": "2.10.0.0",
-      "STACK_VERSION": "2.15.5",
+      "STACK_VERSION": "3.1.1",
       "USE_ZSH_FOR_ROOT": "unset-to-use-ash",
       "SET_LANG": "C.UTF-8",
       "SET_TZ": ""