Remove unnecessary tabIndex from gantt chart SVG rect elements for improved accessibility

[Yugenjr]

This PR removes the tabIndex={0} attribute from gantt chart bar elements that lack corresponding keyboard event handlers, fixing an accessibility anti-pattern that violates WCAG 2.1 guidelines.

Problem
The gantt chart in the HTML reporter renders SVG elements with tabIndex={0}, making them appear focusable and interactive to keyboard and screen reader users. However, these elements have no keyboard event handlers, creating a confusing and broken user experience:

Keyboard users tab onto gantt bars but can't interact with them
Screen readers announce bars as focusable when they're not interactive
Users waste keyboard navigation effort.

Solution
Remove tabIndex={0} from gantt bar elements since they are purely visual timeline indicators with no interactive purpose. The <title> element already provides tooltip accessibility.

Changes Made
File: packages/html-reporter/src/gantt.tsx

Change: Removed tabIndex={0} from SVG rect element (line 157).

fixes #41027

@pavelfeldman kindly consider this tiny minor change

[Skn0tt]

This means that keyboard users cannot tab through the gantt lines anymore, but tabbing did not do anything useful either. So removing it makes us more conformant with WCAG recommendations.

[Yugenjr]

Thanks for reviewing and for the clarification around the WCAG tradeoff. Glad the change aligns better with the expected keyboard accessibility behavior!

[github-actions]

Test results for "MCP"

7207 passed, 1113 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

2 flaky

⚠️ [chromium-library] › library/inspector/recorder-api.spec.ts:120 › should type `@ubuntu-22.04-chromium-tip-of-tree`
⚠️ [firefox-library] › library/inspector/cli-codegen-3.spec.ts:224 › cli codegen › should generate frame locators (4) `@firefox-ubuntu-22.04-node20`

43944 passed, 864 skipped

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Merge workflow run.