ci: run on Go 1.20.x

Author: markus-wa

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
     - name: Install Go
       uses: actions/setup-go@v2
       with:
-        go-version: 1.21.x
+        go-version: 1.20.x
 
     - name: Install Reviewdog
       uses: reviewdog/action-setup@v1