Try fixing on Windows

.bazelci/presubmit.yml

@@ -241,6 +241,7 @@ tasks:
     setup:
       - mkdir C:\b
       - mklink /J C:\b\bazeltest_external %OUTPUT_BASE:/=\%\external
+      - START "" C:\python3\python.exe third_party/local-bazel-registry/server.py
     build_flags:
       - "--config=ci-windows"
     build_targets:
@@ -292,6 +293,7 @@ tasks:
     setup:
       - mkdir C:\b
       - mklink /J C:\b\bazeltest_external %OUTPUT_BASE:/=\%\external
+      - START "" C:\python3\python.exe -m http.server 8000 --directory third_party/local-bazel-registry/
     build_flags:
       - "--config=ci-windows"
       - "--config=windows_arm64"

third_party/local-bazel-registry/server.py

@@ -0,0 +1,23 @@
+import http.server
+import sys
+import threading
+import time
+
+DIRECTORY = "./third_party/local-bazel-registry"
+
+class Handler(http.server.SimpleHTTPRequestHandler):
+  def __init__(self, *args, **kwargs):
+    super().__init__(*args, directory=DIRECTORY, **kwargs)
+
+def _serve(httpd):
+  httpd.serve_forever()
+
+print("creating server...")
+httpd = http.server.HTTPServer(('localhost', 8000), Handler)
+t = threading.Thread(target=_serve, name="httpserver", args=(httpd,))
+print("starting server")
+t.start()
+print("server started, waiting for 10 mins")
+t.join(600)
+print("shutting down...")
+httpd.shutdown()