test: add a regression test for #40510

[dgozman]

The issue was fixed upstream in Chromium.
Closes #40510.

[github-actions]

Test results for "MCP"

1 failed
❌ [firefox] › mcp/annotate.spec.ts:230 › should capture annotations via show --annotate @mcp-macos-latest-firefox

7759 passed, 1249 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

4 flaky

⚠️ [firefox-page] › page/page-emulate-media.spec.ts:144 › should keep reduced motion and color emulation after reload `@firefox-ubuntu-22.04-node20`
⚠️ [firefox-page] › page/page-event-request.spec.ts:181 › should return response body when Cross-Origin-Opener-Policy is set `@firefox-ubuntu-22.04-node20`
⚠️ [webkit-page] › page/page-set-input-files.spec.ts:295 › should detect mime type `@webkit-ubuntu-22.04-node20`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:715 › should indicate current test status `@windows-latest-node22`

50003 passed, 1190 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

The only red is [firefox] › mcp/annotate.spec.ts:230 › should capture annotations via show --annotate, and it flakes on main and other PRs. This PR only adds a regression test to page-network-response.spec.ts, which doesn't touch the MCP annotate flow.

Details

This PR (36865c8) modifies exactly one file — tests/page/page-network-response.spec.ts — adding a regression test for #40510. It changes no product code and nothing the MCP annotate flow exercises.

Pre-existing flake / infra

• [firefox] › mcp/annotate.spec.ts:230 › should capture annotations via show --annotate — flaky across runs. In the test-results DB the Firefox project failed 26 of 664 runs (~4%) and passed the other 638, flipping verdict on SHAs this PR can't be responsible for — PRs fix(webview): support input for elements inside cross-origin <iframe> #41463, devops(test-results-db): CLI to compact CI test results into DuckDB #41673, fix(browsercontext): set closedStatus to closed after close #41806 and several push runs on main (e88063f3, 6f3cce9a, 6693f583, b6357091, 3c711598, d448aac0). It flakes on the other engines too (webkit 16/680, chromium 14/674). Unrelated to a network-response regression test.

_{Triaged by the Playwright bot - agent run}