chore(optimize-svgs): Run Node 20 for SVG optimization action, don't checkout in detached HEAD state

[jdecked]

Problems:

• stefanzweifel/git-auto-commit-action@v4 and thollander/actions-comment-pull-request@v1 run Node 16, which is deprecated for GitHub Actions
• Theoretically, if something went incredibly wrong, the SVG action could generate and commit non-SVG edits
• Attempting to merge changes to a PR branch on push when checked out in detached head state occasionally fails (e.g. this run)

Solutions:

• Bump stefanzweifel/git-auto-commit-action to v5 and thollander/actions-comment-pull-request to v2 which both run Node 20
• Restrict auto-commits to SVG files only
• Check out PR branch in a non-detached HEAD state by specifying the HEAD ref for actions/checkout

[github-actions[bot]]

Optimized 1 SVG(s)

[github-actions[bot]]

Optimized 1 SVG(s)

[github-actions[bot]]

Optimized 1 SVG(s)

[github-actions[bot]]

Optimized 1 SVG(s)

[github-actions[bot]]

Optimized 0 SVG(s)