Fix mirror workflow push permission denied

Add contents: write permission to the workflow so the
GITHUB_TOKEN can push commits, tags, and create releases.

Author: gaborbernat

.github/workflows/main.yaml

@@ -7,6 +7,9 @@ on:
   schedule:
     - cron: "30 8 * * *"
 
+permissions:
+  contents: write
+
 jobs:
   build:
     name: Mirror