Move links to HTTPS to avoid possible 503 errors in broken link checkers

What does this MR do?

Sometimes Amazon returns a 503 error for http links in the book list.

This MR makes these links HTTPS, which hopefully minimises the change Amazon will return 503 to the broken link checkers.

Related issues

Relates to: https://gitlab.com/gitlab-org/gitlab-ce/issues/51696.

Author's checklist

• Apply the correct labels and milestone
• Port the MR to EE (or backport from CE): always recommended, required when the ee-compat-check job fails

Review checklist

• Your team's review (required)
• PM's review (recommended, but not a blocker)
• Technical writer's review (required)
• Merge the EE-MR first, CE-MR afterwards