update flakes installer

.github/workflows/test.yml

@@ -7,13 +7,12 @@ jobs:
   tests:
     strategy:
       matrix:
-        # macOS installer for nixUnstable seems broken atm
-        #os: [ ubuntu-latest, macos-latest ]
         os: [ ubuntu-latest ]
+        # FIXME macos garbage currently collect also nix-shell that runs the test
+        #os: [ ubuntu-latest, macos-latest ]
         nix-install-url:
           - https://nixos.org/nix/install
-          - https://github.com/numtide/nix-flakes-installer/releases/download/nix-2.4pre20200618_377345e/install
-          #- https://github.com/numtide/nix-flakes-installer/releases/download/nix-3.0pre20200804_ed52cf6/install
+          - https://github.com/numtide/nix-flakes-installer/releases/download/nix-2.4pre20201221_9fab14a/install
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2
@@ -21,16 +20,9 @@ jobs:
       with:
         install_url: ${{ matrix.nix-install-url }}
         nix_path: nixpkgs=channel:nixpkgs-unstable
-    - name: Prevent garbage collections of gcroots
-      run:
-        printf "keep-outputs = true\nkeep-derivations = true\nexperimental-features = nix-command flakes\n" | sudo tee -a /etc/nix/nix.conf;
-    - name: Restart nix-daemon with systemctl
-      run:
-        sudo systemctl restart nix-daemon
-      if: matrix.os == 'ubuntu-latest'
-    - name: Restart nix-daemon with launchctl
-      run:
-        sudo launchctl kickstart -k org.nixos.nix-daemon
-      if: matrix.os == 'macos-latest'
+        extra_nix_config: |
+          keep-outputs = true
+          keep-derivations = true
+          experimental-features = nix-command flakes
     - run:
         nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixpkgs-unstable.tar.gz ci.nix --run 'true'