This page has no title frontmatter and no # Heading, so Auto Sidebar titles it from its file name, github-actions-setup.md.
Without titleReplacements
The file name is formatted word by word, capitalising only the first letter of each: "Github Actions Setup".
With titleReplacements
This site passes titleReplacements: { github: 'GitHub' }, so the word github is written as "GitHub" and the sidebar shows GitHub Actions Setup. Keys match whole words, ignoring case, so githubs would be left alone.
Titles an author wrote are never changed by titleReplacements. A page titled "Using github" would keep its lowercase "github".