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

.bcr/presubmit.yml

diff --git a/.bcr/presubmit.yml b/.bcr/presubmit.yml
index fd5f3ba..5eb53ce 100644
--- a/.bcr/presubmit.yml
+++ b/.bcr/presubmit.yml
@@ -6,8 +6,9 @@
       - 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