try to fix scheduled hypothesis test (#9358)

Author: dcherian

.github/workflows/hypothesis.yaml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     if: |
       github.repository == 'pydata/xarray'
-      && (github.event_name == 'push' || github.event_name == 'pull_request')
+      && (github.event_name == 'push' || github.event_name == 'pull_request' || github.event_name == 'schedule')
     outputs:
       triggered: ${{ steps.detect-trigger.outputs.trigger-found }}
     steps: