Stack CI: restrict tests to Linux because of failures

Author: andreasabel

.github/workflows/stack.yml

@@ -54,7 +54,9 @@ jobs:
     - name: Build w/ tests
       run: ${{ env.stack }} test --no-run-tests
 
+    # Tests fail on macOS and Window
     - name: Run tests
+      if: runner.os == 'Linux'
       run: ${{ env.stack }} test
 
     - name: Cache dependencies