ci: also build on aarch64-linux

.github/workflows/test.yml

@@ -7,12 +7,21 @@ on:
       - master
 jobs:
   tests:
-    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          - system: x86_64-linux
+            runner: ubuntu-latest
+          - system: aarch64-linux
+            runner: ubuntu-24.04-arm
+    runs-on: ${{ matrix.runner }}
     steps:
     - uses: actions/checkout@v3
       with:
         fetch-depth: 0
     - uses: cachix/install-nix-action@v31
+      with:
+        extra_nix_config: |
+          extra-systems = ${{ matrix.system }}
     - uses: DeterminateSystems/magic-nix-cache-action@main
-    #- run: nix flake check
-    - run: nix-build -A checks.x86_64-linux.build -A checks.x86_64-linux.validate-openapi
+    - run: nix-build -A checks.${{ matrix.system }}.build -A checks.${{ matrix.system }}.validate-openapi