workflows/scheduled: fix artipacked zizmor findings

We don't need persistent credentials here.

.github/workflows/scheduled.yml

@@ -25,6 +25,7 @@ jobs:
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           fetch-depth: 0
+          persist-credentials: false
           ref: ${{ github.event.pull_request.head.sha }}
 
       - name: Set up Homebrew