chore: suppress verbose review body in Copilot PR reviews

[yury-s]

Summary

• Adds an instruction to .github/copilot-instructions.md telling Copilot not to generate a top-level review body/summary (the "Pull request overview" block with the file table). Findings should go only in inline comments.

Fixes the pattern seen in #39760 (review)

[github-actions]

Test results for "tests 1"

1 failed
❌ [playwright-test] › reporter.spec.ts:251 › merged › should not have internal error when steps are finished after timeout @macos-latest-node20

7 flaky

⚠️ [chromium-library] › library/trace-viewer.spec.ts:1223 › should display language-specific locators `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/video.spec.ts:358 › screencast › should capture navigation `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-page] › page/page-request-continue.spec.ts:754 › propagate headers cross origin redirect after interception `@chromium-ubuntu-22.04-node24`
⚠️ [chromium-library] › library/trace-viewer.spec.ts:1223 › should display language-specific locators `@chromium-ubuntu-22.04-node20`
⚠️ [firefox-library] › library/inspector/cli-codegen-1.spec.ts:1080 › cli codegen › should not throw csp directive violation errors `@firefox-ubuntu-22.04-node20`
⚠️ [webkit-library] › library/screencast.spec.ts:85 › start reuses existing screencast when video recording is running `@webkit-ubuntu-22.04-node20`
⚠️ [playwright-test] › ui-mode-test-output.spec.ts:118 › should collapse repeated console messages for test `@ubuntu-latest-node20`

38813 passed, 845 skipped

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Merge workflow run.

[github-actions]

Test results for "MCP"

5507 passed, 343 skipped

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Merge workflow run.