[Serverless bug bash] Fixes link ref on Install Elastic Defend page (backport #6164)

[mergify]

Serverless bug bash

Resolves #6060.

The same fix has been applied to ESS docs.

Previews

Serverless: Install Elastic Defend

ESS: Install Elastic Defend

---

This is an automatic backport of pull request #6164 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of a6c3736 has failed:

On branch mergify/bp/8.17/pr-6164
Your branch is up to date with 'origin/8.17'.

You are currently cherry-picking commit a6c37361.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   docs/serverless/edr-install-config/install-elastic-defend.asciidoc

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[github-actions]

A documentation preview will be available soon.

• 🔨 Buildkite builds
• 📚 HTML diff
• 📙 Preview page

Request a new doc build by commenting

• Rebuild this PR: run docs-build
• Rebuild this PR and all Elastic docs: run docs-build rebuild

_{run docs-build is much faster than run docs-build rebuild. A rebuild should only be needed in rare situations.}

_{If your PR continues to fail for an unknown reason, the doc build pipeline may be broken. Elastic employees can check the pipeline status here.}