CSP - grammar fix and layout improvements

[hamishwillee]

Fixes #10230

This fixes a minor grammar issue in line 16 (see malware). The rest of the changes just improve the layout for editing readability and add "http" to code blocks where appropriate.

[github-actions]

Preview URLs

• https://pr10298.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTTP/CSP

Flaws

None! 🎉

External URLs

URL: /en-US/docs/Web/HTTP/CSP
Title: Content Security Policy (CSP)
on GitHub

• https://cspscanner.com/ (1 time) (Note! This may be a new URL 👀)
• https://github.com/google/csp-evaluator (1 time) (Note! This may be a new URL 👀)
• https://www.w3.org/TR/CSP/ (1 time) (Note! This may be a new URL 👀)
• https://www.w3.org/TR/CSP2 (1 time) (Note! This may be a new URL 👀)