A11y scorecard fixes

[rezrah]

Summary

Closes https://github.com/github/primer/issues/2857

These changes are required to help turn the Primer accessibility scorecard green. The scorecard uses static code analysis on this repo's source files, and downmarks Primer for lint disable rules beginning with jsx-a11y-*.

List of notable changes:

• Upgrades eslint-plugin-github to 4.10.1 to ensure "All repos are using latest accessibility linting configs"
• Removes all jsx-a11y-* eslint disable rules
  • Remediates missing/broken functionality that led to the eslint rules

What should reviewers focus on?

• Verify that checks pass

Supporting resources (related issues, external links, etc):

• Scorecard

Contributor checklist:

• All new and existing CI checks pass
• Tests prove that the feature works and covers both happy and unhappy paths
• Any drop in coverage, breaking changes or regressions have been documented above
• New visual snapshots have been generated / updated for any UI changes
• All developer debugging and non-functional logging has been removed
• Related issues have been referenced in the PR description

Reviewer checklist:

• Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• Check that tests prove the feature works and covers both happy and unhappy paths
• Check that there aren't other open Pull Requests for the same update/change

Screenshots:

Tests still passing 🟢

[changeset-bot]

🦋 Changeset detected

Latest commit: f01d204

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@primer/react-brand	Patch
@primer/brand-primitives	Patch
@primer/brand-e2e	Patch
@primer/brand-fonts	Patch
@primer/brand-config	Patch
@primer/brand-storybook	Patch

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[github-actions]

🟢 No design token changes found

[github-actions]

🟢 No visual differences found

Our visual comparison tests did not find any differences in the UI.