Flaky tests: fix router navigate URL fragment race

[CoderAbhinav]

What

Fixes #80447.

This fixes a race in the router navigation E2E test should update the URL from the last navigation if only varies in the URL fragment. The test could fail intermittently with the title stuck on "Main" instead of updating to "Link 1":

Error: expect(locator).toHaveText(expected) failed
Locator:  getByTestId('title')
Expected: "Link 1"
Received: "Main"
Timeout:  5000ms
    at test/e2e/specs/interactivity/router-navigate.spec.ts:148

Why

Both navigations in this test target the same page path — they only differ in the URL fragment, which is stripped when building the router's cache key (getPagePath). As a result, both requests go through the same page.route() handler and their resolvers are collected in a shared resolvers array.

Asserting that the pending navigations counter is 2 only guarantees both navigate actions have started (the counter is incremented synchronously in the view action). The actual fetch() calls happen later, inside the router action after a dynamic import(). So resolvers.pop() could release the first navigation's request instead of the last one's, before the second request had even reached the route handler.

That earlier navigation then bails out — its destination is no longer the current one (if ( navigatingTo !== href ) return;) — so nothing re-renders, the title stays "Main", and the assertion for "Link 1" times out.

This is the same class of race that was fixed for the sibling test in this file in #80178.

How

Wait until both requests have reached the route handler before releasing any of them, using a bothRequests barrier that resolves once two resolvers have been collected. Releasing responses only after both requests are intercepted makes the ordering deterministic: the last navigation (the one with the hash) is released first and wins, then the earlier one is released and correctly bails out without replacing the latest HTML.

No production code changes — the router already handles this correctly at runtime; only the test's timing assumptions were unsound.

Testing Instructions

1. Repeat the target test:
   npm run test:e2e -- test/e2e/specs/interactivity/router-navigate.spec.ts -g "should update the URL from the last navigation if only varies in the URL fragment" --repeat-each=30
2. Run the full spec:
   npm run test:e2e -- test/e2e/specs/interactivity/router-navigate.spec.ts

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Co-authored-by: CoderAbhinav <abhinavbelhekar03@git.wordpress.org>

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