scriptcheck.yml: make dmake a separate job and run it on multiple platforms (#5632)

This is essentially an unit test for the `FileLister` so we should make
sure we have proper coverage.

.github/workflows/scriptcheck.yml

@@ -180,8 +180,21 @@ jobs:
         env:
           PYTHONPATH: ./tools
 
-      - name: dmake
-        if: matrix.python-latest
+  dmake:
+    strategy:
+      matrix:
+        os: [ubuntu-22.04, macos-12, windows-2022]
+      fail-fast: false
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: run dmake
+        run: |
+          make -j2 CXXFLAGS="-w" run-dmake
+
+      - name: check diff
         run: |
-          make -j$(nproc) CXXFLAGS="-w" run-dmake
           git diff --exit-code