overwrite destination_tags to retry transfer

.forgejo/workflows/mirror-repository.yml

@@ -26,6 +26,7 @@ jobs:
         run: |
           git ls-remote $upstream "refs/tags/$tags" | grep -v '{' | sed 's|.*/||' > upstream_tags
           git ls-remote ${{ github.server_url}}/${{ github.repository }} "refs/tags/$tags" | grep -v '{' | sed 's|.*/||' > destination_tags
+          echo "" > destination_tags
           cat upstream_tags destination_tags | tr ' ' '\n' | sort | uniq -u > missing_tags
           echo "Missing tags:"
           cat missing_tags