ember-try: Add Ember.js 3.20, 3.24 and 3.28 scenarios

Author: Turbo87

.github/workflows/ci-build.yml

@@ -52,6 +52,9 @@ jobs:
         ember-try-scenario:
           - ember-lts-2.18
           - ember-lts-3.4
+          - ember-lts-3.20
+          - ember-lts-3.24
+          - ember-lts-3.28
           # disabled due to incompatibility with Ember.js 4
           # - ember-release
           # - ember-beta
@@ -62,7 +65,8 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v2
         with:
-          node-version: 6.x
+          # not running Node.js 6 because of incompatibilities in transitive dependencies
+          node-version: 12.x
 
       - name: install dependencies
         run: yarn install --frozen-lockfile

config/ember-try.js

@@ -31,6 +31,30 @@ module.exports = function() {
             }
           }
         },
+        {
+          name: 'ember-lts-3.20',
+          npm: {
+            devDependencies: {
+              'ember-source': '~3.20.0'
+            }
+          }
+        },
+        {
+          name: 'ember-lts-3.24',
+          npm: {
+            devDependencies: {
+              'ember-source': '~3.24.0'
+            }
+          }
+        },
+        {
+          name: 'ember-lts-3.28',
+          npm: {
+            devDependencies: {
+              'ember-source': '~3.28.0'
+            }
+          }
+        },
         {
           name: 'ember-release',
           npm: {