grails-spring-security guide docs publishing uses org.apache.grails:grails-docs-core, but no longer published

### Issue description

We have a problem with grails-spring-security guide docs publishing.

It uses org.apache.grails:grails-docs-core Gradle Plugin to create a release dropdown.
org.apache.grails:grails-docs-core is no longer published, it was removed in: https://github.com/apache/grails-core/pull/15134

It was duplicated to get the grails-spring-security release completed

[Core](https://apache.github.io/grails-spring-security/7.0.x/core-plugin/guide/index.html)
[ACL](https://apache.github.io/grails-spring-security/7.0.x/acl-plugin/guide/index.html)
[CAS](https://apache.github.io/grails-spring-security/7.0.x/cas-plugin/guide/index.html)
[LDAP](https://apache.github.io/grails-spring-security/7.0.x/ldap-plugin/guide/index.html)
[OAuth2](https://apache.github.io/grails-spring-security/7.0.x/oauth2-plugin/guide/index.html)
[REST](https://apache.github.io/grails-spring-security/7.0.x/rest-plugin/guide/index.html)
[UI](https://apache.github.io/grails-spring-security/7.0.x/ui-plugin/guide/index.html)