[8.16](backport #4581) [Synthetics]: fix MFA totp method for browser monitors

[mergify]

Description

• Fix the mfa.totp method which was incorrectly pointing to a method that was changed during the development process and updated incorrectly feat: add support for Time based OTP synthetics#957 (comment)

Documentation sets edited in this PR

Check all that apply.

• Stateful (docs/en/observability/*)
• Serverless (docs/en/serverless/*)
• Integrations Developer Guide (docs/en/integrations/*)
• None of the above

Checklist

• Product/Engineering Review
• Writer Review

---

This is an automatic backport of pull request #4581 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 083cf27 has failed:

On branch mergify/bp/8.16/pr-4581
Your branch is up to date with 'origin/8.16'.

You are currently cherry-picking commit 083cf27f.
  (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)

Changes to be committed:
	modified:   docs/en/observability/synthetics-mfa.asciidoc

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   docs/en/serverless/synthetics/synthetics-mfa.asciidoc

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

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