Harmonize property visibility in Saml2RelyingPartyProperties

Closes gh-19194

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/saml2/Saml2RelyingPartyProperties.java

@@ -59,7 +59,7 @@ public class Saml2RelyingPartyProperties {
 			return this.signing;
 		}
 
-		Identityprovider getIdentityprovider() {
+		public Identityprovider getIdentityprovider() {
 			return this.identityprovider;
 		}