Drop Windows and Bazel 6 from BCR presubmit (#7)

Author: fmeum

.bcr/presubmit.yml

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