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

[Dmitry Gozman (dgozman)]

Summary

• The redirect handler updated the host header via headers['host'] (lowercase-only lookup), while header names preserve their original casing. A Host header set through extraHTTPHeaders was never updated on redirect.
• Now uses the case-insensitive setHeader() helper, consistent with getHeader/removeHeader in the same file.

Fixes#41766

[github-actions]

Test results for "tests 1"

5 flaky

⚠️ [chromium-library] › library/video.spec.ts:664 › screencast › should capture full viewport `@frozen-time-library-chromium-linux`
⚠️ [chromium-library] › library/video.spec.ts:736 › screencast › should work with video+trace `@frozen-time-library-chromium-linux`
⚠️ [chromium-library] › library/video.spec.ts:736 › screencast › should work with video+trace `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/video.spec.ts:699 › screencast › should capture full viewport on hidpi `@realtime-time-library-chromium-linux`
⚠️ [firefox-library] › library/inspector/cli-codegen-3.spec.ts:255 › cli codegen › should generate frame locators (4) `@firefox-ubuntu-22.04-node20`

50370 passed, 1158 skipped

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Merge workflow run.

[github-actions]

Test results for "MCP"

1 failed
❌ [chromium] › mcp/annotate.spec.ts:497 › should disengage annotate mode when --annotate client disconnects @mcp-macos-latest-chromium

7759 passed, 1249 skipped

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Merge workflow run.

[github-actions]

Hi, I'm the Playwright bot and I took a first look at the CI failures.

🟢 The one failure is a pre-existing flake — this PR is clear

mcp/annotate.spec.ts:497 failed on chromium, but it flakes on its own across unrelated SHAs, and this PR only touches fetch redirect header handling — nothing the MCP annotate flow exercises.

Details

This PR changes packages/playwright-core/src/server/fetch.ts to use a case-insensitive Host header lookup on redirect (plus the matching test). The only reported failure is in the MCP annotate suite, which doesn't go anywhere near APIRequestContext redirects.

Pre-existing flake / infra

• [chromium] › mcp/annotate.spec.ts:497 › should disengage annotate mode when --annotate client disconnects — pre-existing flake. Across the test-results DB it flips verdict on every browser: chromium failed 2 of 265 runs, webkit 9/268, firefox 8/261, chrome 5/266 (passed the rest). The two chromium failures are on PR feat(test runner): cancel operations on test end via default abort signal #41707 (run 29078064409) and a push commit (run 29406325712, sha e0e814de) — both unrelated to this PR, so it can't be responsible.

The tests 1 report had 5 flaky, 0 failed, which also don't touch fetch redirects.

_{Triaged by the Playwright bot - agent run}