restore up-to-date condition for no-rebase

since Mergify can't do it or we wouldn't need the label

.github/mergify.yml

@@ -85,6 +85,10 @@ pull_request_rules:
       - label=merge delay passed
       - '#approved-reviews-by>=2'
       - '-label~=^blocked:'
+      # unlike the others, we need to force this one to be up to date
+      # because it's intended for when Mergify doesn't have permission
+      # to rebase
+      - '#commits-behind=0'
 
   # merge+no rebase strategy
   - actions: