Fix the hierarchy of OpenID providers in the docs. (#10445)

changelog.d/10445.doc

@@ -0,0 +1 @@
+Fix hierarchy of providers on the OpenID page.

docs/openid.md

@@ -410,7 +410,7 @@ oidc_providers:
         display_name_template: "{{ user.name }}"
 ```
 
-## Apple
+### Apple
 
 Configuring "Sign in with Apple" (SiWA) requires an Apple Developer account.