chore: setup commit signing when rebasing

Author: Jesper Terkelsen

.github/workflows/rebase.yml

@@ -13,6 +13,10 @@ jobs:
       with:
         fetch-depth: 0 # fetching all history so i can rebase
         token: ${{ secrets.GH_TOKEN }}
+    - name: Configure git for tradeshiftci
+      uses: tradeshift/actions-git/configure-from-gpg-key@v1
+      with:
+        gpg-key: ${{ secrets.TRADESHIFTCI_GPG_KEY }}  
     - uses: tradeshift/rebase-upstream-action@master
       # with:  # all args are optional
       #   upstream: <user>/<repo>