fix: create /nix when installing nix on root runners

.gitea/workflows/kubeadm-bootstrap.yml

@@ -99,6 +99,11 @@ jobs:
           fi
 
           echo "Nix missing; installing no-daemon Nix for this runner job"
+          if [ "$(id -u)" -eq 0 ]; then
+            mkdir -p /nix
+            chown root:root /nix
+            chmod 0755 /nix
+          fi
           sh <(curl -L https://nixos.org/nix/install) --no-daemon
 
           if [ -f "$HOME/.nix-profile/etc/profile.d/nix.sh" ]; then

.gitea/workflows/terraform-apply.yml

@@ -100,6 +100,11 @@ jobs:
           NIX_CONFIG: experimental-features = nix-command flakes
         run: |
           if [ ! -x /nix/var/nix/profiles/default/bin/nix ] && ! command -v nix >/dev/null 2>&1; then
+            if [ "$(id -u)" -eq 0 ]; then
+              mkdir -p /nix
+              chown root:root /nix
+              chmod 0755 /nix
+            fi
             sh <(curl -L https://nixos.org/nix/install) --no-daemon
           fi