Define base branch

Author: theletterf

.github/workflows/sync-sheets-keyless.yml

@@ -60,6 +60,7 @@ jobs:
         uses: peter-evans/create-pull-request@c0f553fe549906ede9cf27b5156039d195d2ece0 # v8.1.0
         with:
           token: ${{ github.token }}
+          base: main
           branch: automated/sheets-sync
           delete-branch: true
           title: "Update CSV from Google Sheets"