workflows/check-shell: use job matrix

.github/workflows/check-shell.yml

@@ -9,21 +9,19 @@ on:
 permissions: {}
 
 jobs:
-  x86_64-linux:
-    name: shell-check-x86_64-linux
-    runs-on: ubuntu-24.04
-    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
-        with:
-          # pull_request_target checks out the base branch by default
-          ref: refs/pull/${{ github.event.pull_request.number }}/merge
-      - uses: cachix/install-nix-action@08dcb3a5e62fa31e2da3d490afc4176ef55ecd72 # v30
-      - name: Build shell
-        run: nix-build shell.nix
+  shell-check:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - runner: ubuntu-24.04
+            system: x86_64-linux
+          - runner: macos-14
+            system: aarch64-darwin
+
+    name: shell-check-${{ matrix.system }}
+    runs-on: ${{ matrix.runner }}
 
-  aarch64-darwin:
-    name: shell-check-aarch64-darwin
-    runs-on: macos-14
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with: