Fix mergify - new builds

also see: https://github.com/pystatgen/sgkit/pull/100#issuecomment-690319548

Author: ravwojdyla

.mergify.yml

@@ -2,7 +2,8 @@ pull_request_rules:
   - name: automatic merge
     conditions:
       - base=master
-      - status-success=build
+      - status-success=build (3.7)
+      - status-success=build (3.8)
       - approved-reviews-by=@pystatgen/committers
       - "#approved-reviews-by>=1"
       - label=auto-merge