CI: disable persist-credentials for actions/checkout

It is a possible security issue.
We do not want to persist credentials in the repo and thus exposing those
to further steps.

References:

actions/checkout#485 (comment)
azat/chdig#67

.github/workflows/ci-tests.yml

@@ -10,6 +10,7 @@ jobs:
             - uses: actions/checkout@v4
               with:
                 submodules: true
+                persist-credentials: false
 
             - uses: actions/cache@v4
               with: