Update actions/checkout action to v3

Author: renovate-bot

.github/workflows/ci.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Setup Ember Testing
         uses: mydea/actions-ember-testing@v2
       - name: Checkout Repo
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Set Yarn Cache Directory
         id: yarn-cache-dir
         run: echo "::set-output name=dir::$(yarn cache dir)"

.github/workflows/publish.yml

@@ -11,7 +11,7 @@ jobs:
   publish:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: actions/setup-node@v3
         with:
           node-version: '10.x'