.gitea/workflows: update actions/checkout: v3 -> v6

.gitea/workflows/eval.yml

@@ -4,9 +4,9 @@ on:
   push:
 jobs:
   evals:
-    runs-on: ubuntu-latest
+    runs-on: debian-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v6
     - run: apt-get update && apt-get -y install sudo
     - uses: https://github.com/cachix/install-nix-action@v31
     - run: echo -e "show-trace = true\nmax-jobs = auto\ntrusted-users = root\nexperimental-features = nix-command flakes\nbuild-users-group =" > /etc/nix/nix.conf