Drop support for Ember < 3.28

Author: mansona

.github/workflows/ci.yml

@@ -63,9 +63,6 @@ jobs:
       fail-fast: false
       matrix:
         try-scenario:
-          - ember-lts-3.16
-          - ember-lts-3.20
-          - ember-lts-3.24
           - ember-lts-3.28
           - ember-release
           - ember-beta

config/ember-try.js

@@ -6,30 +6,6 @@ const { embroiderSafe, embroiderOptimized } = require('@embroider/test-setup');
 module.exports = async function () {
   return {
     scenarios: [
-      {
-        name: 'ember-lts-3.16',
-        npm: {
-          devDependencies: {
-            'ember-source': '~3.16.0',
-          },
-        },
-      },
-      {
-        name: 'ember-lts-3.20',
-        npm: {
-          devDependencies: {
-            'ember-source': '~3.20.5',
-          },
-        },
-      },
-      {
-        name: 'ember-lts-3.24',
-        npm: {
-          devDependencies: {
-            'ember-source': '~3.24.3',
-          },
-        },
-      },
       {
         name: 'ember-lts-3.28',
         npm: {