MAINT: adjust cron to twice a week

Author: andyfaff

.github/workflows/wheels.yml

@@ -14,7 +14,7 @@ on:
     #        │  │ │ ┌───────────── month (1 - 12 or JAN-DEC)
     #        │  │ │ │ ┌───────────── day of the week (0 - 6 or SUN-SAT)
     #        │  │ │ │ │
-    - cron: "9  9 * * MON"
+    - cron: "9  9 * * 1,4"
   pull_request:
     branches:
       - main