test: skip flaky BroadcastChannel relay test (#2476)

## Summary
- Skip the flaky `relays Coinbase events via BroadcastChannel` test that
causes intermittent CI failures
- BroadcastChannel delivery timing is unreliable in vitest's jsdom
environment

## Test plan
- [x] All other coinbase-popup tests still pass
- [x] CI should no longer have intermittent failures from this test

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: broody

packages/keychain/src/components/coinbase-popup.test.tsx

@@ -110,7 +110,8 @@ describe("CoinbasePopup", () => {
     expect(screen.queryByText("Payment processing...")).not.toBeInTheDocument();
   });
 
-  it("relays Coinbase events via BroadcastChannel", async () => {
+  // TODO: flaky test - BroadcastChannel delivery timing is unreliable in vitest
+  it.skip("relays Coinbase events via BroadcastChannel", async () => {
     const { channel, messages } = listenOnChannel();
 
     renderPopup();