ci: fix TOB-SCREUC-8, do not persist git credentials

[Thegaram]

Fix multiple zizmor error like this:

warning[artipacked]: credential persistence through GitHub Actions artifacts
  --> .github/workflows/contracts.yml:30:9
   |
30 |         - name: Checkout sources
   |  _________-
31 | |         uses: actions/checkout@v4
32 | |         with:
33 | |           submodules: recursive
   | |_______________________________- does not set persist-credentials: false
   |
   = note: audit confidence → Low

The base branch was changed.