fix: do not allow to override cookie header

[yury-s]

Behavior before this PR regarding 'Cookie' header already varied between browsers:

• Chromium would not respect the 'Cookie' header if there was one with the same name in its cookie jar
• WebKit would also take one from the cookie jar
  To override cookies addCookies should be used instead.

Reference #35154

[zuzusik]

I can't agree this closes #35154

This adds tests to existing functionality, but I believe it has a bug, which is clearly reproduced in the repo linked to #35154

[github-actions]

Test results for "tests 1"

13 failed
❌ [chromium-library] › tests/library/har.spec.ts:276:3 › should record request overrides @chromium-ubuntu-22.04-node18
❌ [chromium-library] › tests/library/har.spec.ts:486:3 › should record failed request overrides @chromium-ubuntu-22.04-node18
❌ [chromium-library] › tests/library/har.spec.ts:276:3 › should record request overrides @chromium-ubuntu-22.04-node20
❌ [chromium-library] › tests/library/har.spec.ts:486:3 › should record failed request overrides @chromium-ubuntu-22.04-node20
❌ [chromium-library] › tests/library/har.spec.ts:276:3 › should record request overrides @chromium-ubuntu-22.04-node22
❌ [chromium-library] › tests/library/har.spec.ts:486:3 › should record failed request overrides @chromium-ubuntu-22.04-node22
❌ [firefox-library] › tests/library/har.spec.ts:276:3 › should record request overrides @firefox-ubuntu-22.04-node18
❌ [firefox-library] › tests/library/har.spec.ts:486:3 › should record failed request overrides @firefox-ubuntu-22.04-node18
❌ [firefox-page] › tests/page/page-route.spec.ts:169:3 › should override cookie header @firefox-ubuntu-22.04-node18
❌ [chromium-library] › tests/library/har.spec.ts:276:3 › should record request overrides @ubuntu-22.04-chromium-tip-of-tree
❌ [chromium-library] › tests/library/har.spec.ts:486:3 › should record failed request overrides @ubuntu-22.04-chromium-tip-of-tree
❌ [webkit-library] › tests/library/har.spec.ts:276:3 › should record request overrides @webkit-ubuntu-22.04-node18
❌ [webkit-library] › tests/library/har.spec.ts:486:3 › should record failed request overrides @webkit-ubuntu-22.04-node18

2 flaky

⚠️ [firefox-page] › tests/page/page-evaluate.spec.ts:403:3 › should throw for too deep reference chain @firefox-ubuntu-22.04-node18
⚠️ [chromium] › tests/headerView.spec.tsx:43:1 › should toggle filters @web-components-html-reporter

38738 passed, 807 skipped
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Merge workflow run.