ci: add fish 3.6.0 job (based on alpine edge)

see pure-fish/docker-fish#5

.github/workflows/ci.yml

@@ -32,6 +32,7 @@ jobs:
             { fish: 3.3.1, alpine: 3.15 },
             { fish: 3.4.1, alpine: 3.16 },
             { fish: 3.5.1, alpine: 3.17 },
+            { fish: 3.6.0, alpine: 'edge' },
           ]
     steps:
       - uses: actions/checkout@v2