fix(test): make test_google_endpoint_routing resilient to module reloads (#24499)

Same root cause as test_end_user_jwt_auth: test_cors_config reloads
proxy_server module, so initialize() sets llm_router on the old module
while the test's patch target resolves to the new one where it's None.

Fix by syncing llm_router from the original module to the live
sys.modules entry after initialize().

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>