fix(fetch): use case-insensitive host header lookup on redirect

[rahulrao85]

Summary

The redirect host header update used \headers['host']\ (lowercase only), but \setHeader()\ preserves the original casing of header names. If \extraHTTPHeaders\ set 'Host'\ (capital H), the host was never updated on redirect, causing the request to be sent with the original origin's Host header.

Now uses case-insensitive lookup (\Object.keys().find()), consistent with \setHeader, \getHeader, and
emoveHeader\ in the same file.

Fixes: #41766

[dgozman]

Thank you for the PR, this looks good.

Could you please use the helper function and update the should update host header on redirect test in tests/library/browsercontext-fetch.spec.ts to pass HosT instead of host?

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[github-actions]

Test results for "MCP"

3 failed
❌ [chrome] › mcp/annotate.spec.ts:497 › should disengage annotate mode when --annotate client disconnects @mcp-macos-latest-chrome
❌ [firefox] › mcp/annotate.spec.ts:173 › user-initiated annotate downloads zip with feedback.md @mcp-macos-latest-firefox
❌ [firefox] › mcp/annotate.spec.ts:447 › should switch screencast to -s session on show --annotate @mcp-macos-latest-firefox

7757 passed, 1249 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

9 flaky

⚠️ [chromium-library] › library/video.spec.ts:736 › screencast › should work with video+trace `@frozen-time-library-chromium-linux`
⚠️ [chromium-library] › library/video.spec.ts:294 › screencast › should capture navigation `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/video.spec.ts:495 › screencast › should capture static page in persistent context @smoke `@chromium-ubuntu-22.04-node24`
⚠️ [chromium-library] › library/har-websocket.spec.ts:231 › should embed websocket messages `@chromium-ubuntu-22.04-node20`
⚠️ [chromium-library] › library/video.spec.ts:294 › screencast › should capture navigation `@chromium-ubuntu-22.04-node20`
⚠️ [chromium-library] › library/chromium/chromium.spec.ts:299 › should report intercepted service worker requests in HAR `@chromium-ubuntu-22.04-node22`
⚠️ [chromium-library] › library/video.spec.ts:356 › screencast › should work for popups `@chromium-ubuntu-22.04-node22`
⚠️ [firefox-library] › library/heap.spec.ts:223 › should not leak workers `@firefox-ubuntu-22.04-node20`
⚠️ [firefox-page] › page/page-emulate-media.spec.ts:144 › should keep reduced motion and color emulation after reload `@firefox-ubuntu-22.04-node20`

49676 passed, 1156 skipped

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Merge workflow run.