tools: add read-only access in nix-changes.yml

Without it, the workflow fails on private forks.

Signed-off-by: Antoine du Hamel <duhamelantoine1995@gmail.com>
PR-URL: #66691
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ulises Gascón <ulisesgascongonzalez@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: aduh95

.github/workflows/nix-changes.yml

@@ -48,7 +48,7 @@ jobs:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
         with:
           fetch-depth: 2
-          persist-credentials: false
+          persist-credentials: true # We need read access in case we need to fetch in `Compute requisites before change` step
           sparse-checkout: |
             shell.nix
             tools/nix/