Fix OAuth2 Login Reference Format

Issue: gh-5836

docs/manual/src/docs/asciidoc/_includes/servlet/preface/java-configuration.adoc

@@ -448,10 +448,10 @@ spring:
 ----
 +
 .OAuth Client properties
-===
+====
 <1> `spring.security.oauth2.client.registration` is the base property prefix for OAuth Client properties.
 <2> Following the base property prefix is the ID for the <<jc-oauth2login-client-registration,ClientRegistration>>, such as google.
-===
+====
 
 . Replace the values in the `client-id` and `client-secret` property with the OAuth 2.0 credentials you created earlier.