[Fundamentals] Add GitHub Secret Scanning details to token formats page

[ethulia]

Summary

Screenshots (optional)

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/content/docs/fundamentals/	@dcpena, @cloudflare/pcx-technical-writing

[ethulia]

/bonk review this

[ask-bonk]

No issues found. The changes add clear, accurate details about GitHub Secret Scanning behavior and follow the documentation style guide.

[ask-bonk]

No issues found. The changes add clear, accurate details about GitHub Secret Scanning behavior and follow the documentation style guide.

Review summary:

• MDX syntax is valid with no unescaped characters
• Frontmatter fields are correct
• External link to GitHub docs is appropriate
• Heading hierarchy is properly structured (H2 → H3)
• Active voice used throughout, no contractions
• Content accurately distinguishes between public and private repository handling

Approved — PR is ready for merge.

github run

[github-actions]

Preview URL: https://99b90097.preview.developers.cloudflare.com
Preview Branch URL: https://mlu-scannable-tokens-secret-scanning.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/fundamentals/api/get-started/token-formats/	https://mlu-scannable-tokens-secret-scanning.preview.developers.cloudflare.com/fundamentals/api/get-started/token-formats/