Add checkout step to release

Author: mac-cain13

.github/workflows/release.yml

@@ -11,6 +11,8 @@ jobs:
   publish:
     runs-on: macos-latest
     steps:
+    - name: Checkout
+      uses: actions/checkout@v2
     - name: Publish to Cocoapods
       run: |
         export POD_VERSION=$(echo $TAG_NAME | cut -c2-)