try this

.github/workflows/build-sd-image.yml

@@ -8,10 +8,16 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
+
+      - name: Install QEMU
+        run: sudo apt-get install qemu-user-static
 
       - name: Install Nix
-        uses: cachix/install-nix-action@v16
+        uses: cachix/install-nix-action@v21
+        with:
+          extra_nix_config: |
+            system = aarch64-linux
 
       - name: Build SD image
         run: nix build -L '.#nixosConfigurations.pochita-sd.config.system.build.sdImage'