Fix Antora Warnings

Closes gh-13210

Author: rwinch

docs/modules/ROOT/pages/reactive/oauth2/login/advanced.adoc

@@ -207,7 +207,7 @@ The Redirection Endpoint is used by the Authorization Server for returning the A
 OAuth 2.0 Login leverages the Authorization Code Grant.
 Therefore, the authorization credential is the authorization code.
 
-The default Authorization Response redirection endpoint is `/login/oauth2/code/{registrationId}`.
+The default Authorization Response redirection endpoint is `+/login/oauth2/code/{registrationId}+`.
 
 If you would like to customize the Authorization Response redirection endpoint, configure it as shown in the following example:
 
@@ -739,5 +739,5 @@ class OAuth2LoginSecurityConfig {
 ----
 ====
 
-NOTE: `OidcClientInitiatedServerLogoutSuccessHandler` supports the `{baseUrl}` placeholder.
+NOTE: `OidcClientInitiatedServerLogoutSuccessHandler` supports the `+{baseUrl}+` placeholder.
 If used, the application's base URL, like `https://app.example.org`, will replace it at request time.

docs/modules/ROOT/pages/servlet/oauth2/login/advanced.adoc

@@ -928,5 +928,5 @@ class OAuth2LoginSecurityConfig : WebSecurityConfigurerAdapter() {
 ----
 ====
 
-NOTE: `OidcClientInitiatedLogoutSuccessHandler` supports the `{baseUrl}` placeholder.
+NOTE: `OidcClientInitiatedLogoutSuccessHandler` supports the `+{baseUrl}+` placeholder.
 If used, the application's base URL, like `https://app.example.org`, will replace it at request time.