[skip ci] ci: schedule recurring CI and CIBW runs (#6048)

Run ci.yml and tests-cibw.yml twice weekly so master bitrot is easier to spot and root-cause before weekend maintenance.

Co-authored-by: Cursor <cursoragent@cursor.com>

.github/workflows/ci.yml

@@ -1,6 +1,9 @@
 name: CI
 
 on:
+  # Run on Wednesday and Friday at 06:17 UTC.
+  schedule:
+    - cron: "17 6 * * 3,5"
   workflow_dispatch:
   pull_request:
     types:

.github/workflows/tests-cibw.yml

@@ -1,6 +1,9 @@
 name: CIBW
 
 on:
+  # Run on Wednesday and Friday at 06:47 UTC.
+  schedule:
+    - cron: "47 6 * * 3,5"
   workflow_dispatch:
   pull_request:
     branches: