run tests against Ember v5.12 in CI (#292)

Author: jelhan

.github/workflows/ci.yml

@@ -53,7 +53,7 @@ jobs:
           - ember-lts-4.4
           - ember-lts-4.8
           - ember-lts-4.12
-          - ember-lts-5.4
+          - ember-lts-5.12
           - ember-release
           - ember-beta
           - ember-canary

test-app/config/ember-try.js

@@ -46,10 +46,10 @@ module.exports = async function () {
         },
       },
       {
-        name: 'ember-lts-5.4',
+        name: 'ember-lts-5.12',
         npm: {
           devDependencies: {
-            'ember-source': '~5.4.0',
+            'ember-source': '~5.12.0',
           },
         },
       },