Fix Size Comparison Comment (#2657)

* Make sure checking out repository first.

.github/workflows/post-size-cmp.yml

@@ -13,6 +13,9 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
+      - name: Download Repository
+        uses: actions/checkout@v2
+
       - if: github.event.workflow_run.event == 'pull_request'
         name: Download Artifact
         uses: Legit-Labs/action-download-artifact@v2
@@ -23,9 +26,6 @@ jobs:
           name: size-cmp-info
           path: "size-cmp-info/"
 
-      - name: Download Repository
-        uses: actions/checkout@v2
-
       - name: Make pull request comment
         run: python3 ci/make_example_size_cmt.py