temp: test downstream on Windows

Author: radoering

.github/workflows/downstream.yml

@@ -8,9 +8,10 @@ on:
 jobs:
   tests:
     name: ${{ matrix.ref }}
-    runs-on: ubuntu-latest
+    runs-on: "${{ matrix.os }}-latest"
     strategy:
       matrix:
+        os: [Ubuntu, Windows]
         ref: ["refs/pull/6616/head"]
       fail-fast: false
     defaults: