move nixbuild key to another path, configure ssh_config from file in repo

Author: Lillecarl

.github/actions/setup-nix/action.yaml

@@ -41,8 +41,6 @@ runs:
     - name: Configure SSH Keys
       shell: bash
       run: |
-        mkdir -p ~/.ssh
-        echo "${{ inputs.nixbuild_key }}" > ~/.ssh/id_ed25519
-        chmod 600 ~/.ssh/id_ed25519
-        echo -e "Host *\n\tStrictHostKeyChecking no" | sudo tee -a ~/.ssh/config > /dev/null
+        echo "${{ inputs.nixbuild_key }}" | install -D -m 600 /dev/stdin ~/.ssh/nixbuild_key
+        install -m 644 "${{ github.workspace }}/.github/assets/ssh-config" ~/.ssh/config
 

.github/assets/ssh-config

@@ -0,0 +1,4 @@
+Host eu.nixbuild.net
+  IdentityFile ~/.ssh/nixbuild_key
+Host *
+  StrictHostKeyChecking no