Test Bazel 6 and Windows in BCR presubmit (#11)

Author: fmeum

.bcr/presubmit.yml

@@ -6,9 +6,8 @@ bcr_test_module:
       - debian10
       - ubuntu2004
       - macos
-      # Reenable after making private APIs available in 7.4.0.
-      # - windows
-    bazel: [7.x]
+      - windows
+    bazel: [6.x, 7.x]
   tasks:
     run_test_module:
       name: Run test module