Remove deprecated usage of WebTestClientBuilderCustomizer

See gh-19536

Author: dreis2211

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/restdocs/RestDocsWebTestClientBuilderCustomizer.java

@@ -16,7 +16,7 @@
 
 package org.springframework.boot.test.autoconfigure.restdocs;
 
-import org.springframework.boot.test.autoconfigure.web.reactive.WebTestClientBuilderCustomizer;
+import org.springframework.boot.test.web.reactive.server.WebTestClientBuilderCustomizer;
 import org.springframework.restdocs.webtestclient.WebTestClientRestDocumentationConfigurer;
 import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.util.StringUtils;