renamed ssh key in action script

.forgejo/workflows/nix_build.yaml

@@ -32,20 +32,20 @@ jobs:
 
       - name: nix flake archive
         run: |
-          cat <<EOF > .id_rsa
+          cat <<EOF > .ssh_key
           ${{ secrets.SSH_KEY }}
           EOF
-          chmod 600 .id_rsa
+          chmod 600 .ssh_key
 
           eval $(ssh-agent)
-          ssh-add .id_rsa
+          ssh-add .ssh_key
 
           nix flake archive
           nix flake check --verbose --log-format raw
 
           echo $SSH_AGENT_PID
           kill $SSH_AGENT_PID
-          rm .id_rsa
+          rm .ssh_key
 
       - name: nix build orbi
         run: nix build .#nixosConfigurations.orbi.config.system.build.toplevel