Fix merge conflict

Author: jgrandja

oauth2/oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/authentication/OAuth2AuthorizationCodeRequestAuthenticationException.java

@@ -18,7 +18,8 @@
 
 import java.io.Serial;
 
-import org.springframework.lang.Nullable;
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.security.core.Authentication;
 import org.springframework.security.oauth2.core.OAuth2AuthenticationException;
 import org.springframework.security.oauth2.core.OAuth2Error;