Use 8 Windows CI VMs instead of 4.
diff --git a/buildkite/create_instances.py b/buildkite/create_instances.py
index 984b77b..da4e7e0 100755
--- a/buildkite/create_instances.py
+++ b/buildkite/create_instances.py
@@ -71,7 +71,7 @@
         'service_account': 'bazel-release-process@bazel-public.iam.gserviceaccount.com',
     },
     'buildkite-windows': {
-        'count': 4,
+        'count': 8,
         'image_family': 'buildkite-windows',
         'local_ssd': 'interface=scsi',
         'metadata_from_file': 'windows-startup-script-ps1=startup-windows.ps1',