ci: manual nixsgx cache upload

Signed-off-by: Harald Hoyer <harald@matterlabs.dev>

.github/workflows/cachix.yml

@@ -0,0 +1,37 @@
+name: cachix
+
+on:
+  pull_request:
+    branches: [ "main" ]
+  push:
+    branches: ["main"]
+  workflow_dispatch:
+    inputs:
+      target_branch:
+        description: "Target branch to upload cachix"
+        type: string
+        required: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4
+      - uses: cachix/install-nix-action@v27
+        with:
+          extra_nix_config: |
+            access-tokens = github.com=${{ github.token }}
+      - uses: cachix/cachix-action@v15
+        with:
+          name: nixsgx
+          authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
+      - name: Enable magic Nix cache
+        uses: DeterminateSystems/magic-nix-cache-action@main
+
+      - name: nix build
+        run: nix run github:nixos/nixpkgs/nixos-23.11#nixci
+
+      - name: manual cachix upload
+        run: |
+          a=($(nix flake show --accept-flake-config --json | jq -r ".packages.\"x86_64-linux\" | keys | @sh" | tr -d \\\' ))
+          nix build --accept-flake-config --json "${a[@]/#/.#}" | jq -r '.[].outputs | to_entries[].value' | cachix push nixsgx