docs: Move authentication-methods#ldap anchor to appropriate heading.

Commit 30eaed0378 (#15001) incorrectly
inserted a different section between the anchor and the heading.

Signed-off-by: Anders Kaseorg <anders@zulip.com>
(cherry picked from commit c3646ec67f)

docs/production/authentication-methods.md

@@ -35,6 +35,9 @@ Each of these requires one to a handful of lines of configuration in
 `settings.py`, as well as a secret in `zulip-secrets.conf`.  Details
 are documented in your `settings.py`.
 
+```eval_rst
+.. _ldap:
+```
 ## LDAP (including Active Directory)
 
 Zulip supports retrieving information about users via LDAP, and
@@ -473,10 +476,6 @@ authenticate the user to when they visit your SSO URL from the IdP.
 (If the organization is on the root domain, use the empty string:
 `{"subdomain": ""}`.).
 
-```eval_rst
-.. _ldap:
-```
-
 ### Restricting access to specific organizations
 
 If you're hosting multiple Zulip organizations, you can restrict which