ci: disable persist-credentials for actions/checkout in system-tests

Author: cbeauchesne

Diff for: .github/workflows/system-tests.yml

@@ -35,6 +35,7 @@ jobs:
         with:
           repository: 'DataDog/system-tests'
           ref: ${{ env.ST_REF }}
+          persist-credentials: false
       - name: Pull released image
         run: |
           if docker pull ${{ env.REPO }}/system-tests/${{ matrix.image.name }}:latest; then
@@ -106,12 +107,14 @@ jobs:
         with:
           repository: 'DataDog/system-tests'
           ref: ${{ env.ST_REF }}
+          persist-credentials: false
       - name: Checkout ${{ matrix.library.repository }}
         uses: actions/checkout@v4
         with:
           repository: '${{ matrix.library.repository }}'
           path: 'binaries/${{ matrix.library.path }}'
           fetch-depth: 2
+          persist-credentials: false
       - name: Pull released image
         run: |
           if docker pull ${{ env.REPO }}/system-tests/${{ matrix.library.name }}/${{ matrix.image }}-${{ matrix.app }}:latest; then
@@ -252,6 +255,7 @@ jobs:
         with:
           repository: 'DataDog/system-tests'
           ref: ${{ env.ST_REF }}
+          persist-credentials: false
       - name: Pull runner image
         run: |
           docker pull ${{ env.REPO }}/system-tests/runner:gha${{ github.run_id }}-g${{ github.sha }}
@@ -317,6 +321,7 @@ jobs:
         with:
           repository: 'DataDog/system-tests'
           ref: ${{ env.ST_REF }}
+          persist-credentials: false
       - name: Retrieve logs
         uses: actions/download-artifact@v4
         with: