fix: update actions improved repository checkout configuration

.github/workflows/pr-preview.yml

@@ -19,7 +19,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
+        with:
+          repository: ${{ github.repository }}
+          ref: refs/pull/${{ github.event.pull_request.number }}/merge
+          fetch-depth: 1
+          persist-credentials: false
 
       - name: Setup Flutter
         if: github.event.action != 'closed'

.github/workflows/pr-unit-tests.yml

@@ -26,11 +26,18 @@ jobs:
         uses: actions/checkout@v6
         continue-on-error: true
         id: checkout_https
+        with:
+          repository: ${{ github.repository }}
+          ref: refs/pull/${{ github.event.pull_request.number }}/merge
+          fetch-depth: 1
+          persist-credentials: false
 
       - name: Checkout repository via SSH (fallback)
         if: steps.checkout_https.outcome == 'failure'
         uses: actions/checkout@v6
         with:
+          repository: ${{ github.repository }}
+          ref: refs/pull/${{ github.event.pull_request.number }}/merge
           ssh-key: ${{ secrets.SSH_PRIVATE_KEY }}
           ssh-strict: false