fix: keep GitHub annotations parseable with dot reporter

[mturac]

Fixes #41272.

Summary

This keeps GitHub failure annotations parseable when the GitHub reporter is combined with reporters that leave output on the current line, such as the dot reporter.

The fix emits a line break before per-test GitHub failure annotations, so the ::error workflow command starts at the beginning of a line. It also adds a regression for reporter: "dot,github" to ensure the annotation is not written inline after the dot reporter output.

Validation

• npm run ttest -- reporter-github.spec.ts
• npx eslint packages/playwright/src/reporters/github.ts tests/playwright-test/reporter-github.spec.ts
• npm run tsc -- --pretty false
• npm run build
• git diff --check

[mturac]

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