drop support for ember-power-select v4 and v5

Author: jelhan

.github/workflows/ci.yml

@@ -66,7 +66,6 @@ jobs:
           - ember-canary
           - ember-default-with-jquery
           - ember-classic
-          - ember-power-select-v4
     steps:
       - name: Checkout code
         uses: actions/checkout@v3

README.md

@@ -10,7 +10,7 @@ forms.
 Compatibility
 ------------------------------------------------------------------------------
 
-* Ember Power Select v4 or above
+* Ember Power Select v6 or above
 * Ember Bootstrap v5 or above
 * Ember.js v3.28 or above
 * Ember CLI v3.16 or above

config/ember-try.js

@@ -98,14 +98,6 @@ module.exports = async function () {
       },
       embroiderSafe(),
       embroiderOptimized(),
-      {
-        name: 'ember-power-select-v4',
-        npm: {
-          devDependencies: {
-            'ember-power-select': '^4.1.7',
-          },
-        },
-      },
     ],
   };
 };