fix CI

.github/workflows/tests.yml

@@ -16,6 +16,9 @@ jobs:
         uses: actions/setup-node@v2
         with:
           node-version: ${{ matrix.node-version }}
+      - name: Install globally ember-cli
+        run: |
+          npm i -g ember-cli@3.28.0
       - name: Install dependencies
         run: |
           npm i