Fixed typo in Web Security Basics essay

[rdbo]

Description

This PR simply fixes the typo "Hypermdia" in the Web Security Basics with HTMX essay. Nothing fancy, but hey.

Corresponding issue: N/A

Checklist

• [x] I have read the contribution guidelines
• [x] I have targeted this PR against the correct branch (master for website changes, dev for source changes)
• [x] This is either a bugfix, a documentation update, or a new feature that has been explicitly approved via an issue
• [ ] I ran the test suite locally (npm run test) and verified that it succeeded