DAOS-16262 ci: Run Bullseye workflow on schedule (#15574)

Saturdays at midnight, UTC.

Signed-off-by: Brian J. Murrell <[email protected]>

.github/workflows/bullseye-coverage.yml

@@ -42,11 +42,9 @@ on:
       functional-test-distros:
         description: 'Distros to run Functional testing on (i.e. el8 el9 leap15, etc.)'
         required: false
-  pull_request:
-  push:
-    branches:
-      - master
-      - 'release/*'
+  schedule:
+    - cron: "0 0 * * 6"     # Every Saturday
+
 
 concurrency:
   group: bullseye-coverage-${{ github.head_ref  || github.run_id }}