test(infinite-scroll): stabilize top scroll test

[ManthanBhatt]

Issue number: resolves #30423

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What is the current behavior?

The top-positioned infinite scroll test is flaky on CI with Safari and is currently skipped for WebKit. The test assumes a specific initial scroll state, which makes it timing-sensitive.

What is the new behavior?

The test now uses a deterministic scroll sequence by scrolling to the bottom first, waiting for the content to actually be offset, and then scrolling back to the top before waiting for ionInfiniteComplete.

• remove the WebKit skip
• ensure the test starts from a known scrolled state
• keep the existing item-count assertion after loading more content

Does this introduce a breaking change?

• Yes
• No

Other information

• Verified locally with npx playwright test src/components/infinite-scroll/test/top/infinite-scroll.e2e.ts --project="Mobile Chrome"
• Verified locally with npx playwright test src/components/infinite-scroll/test/top/infinite-scroll.e2e.ts --project="Mobile Safari"
• npx eslint src/components/infinite-scroll/test/top/infinite-scroll.e2e.ts passed

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