fix(test-runner): match file paths containing spaces on Windows

[yury-s]

Summary

• On Windows, createFileMatcher falls back to a forward-slash form to handle unix-style paths from Cygwin / Git Bash. It used url.pathToFileURL(), which percent-encodes spaces, so an absolute CLI arg like C:/test dir/example.spec.mjs never matched the collected file C:\test dir\example.spec.mjs (file URL contains test%20dir).
• Replace the URL conversion with a plain separator normalization (filePath.split(path.sep).join('/')) so spaces (and other URL-reserved characters) are preserved.

Fixes #40767

[github-actions]

Test results for "MCP"

1 failed
❌ [firefox] › mcp/cli-session.spec.ts:99 › session stops when browser exits @mcp-windows-latest-firefox

7056 passed, 1068 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

2 flaky

⚠️ [chromium-library] › library/video.spec.ts:647 › screencast › should capture full viewport `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/video.spec.ts:719 › screencast › should work with video+trace `@chromium-ubuntu-22.04-node24`

41751 passed, 850 skipped

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Merge workflow run.