Polish "Remove usages of BasicAuthorizationInterceptor"

Closes gh-14830

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/client/RestTemplateBuilderTests.java

@@ -330,6 +330,16 @@ public class RestTemplateBuilderTests {
 		assertThat(interceptor).extracting("password").containsExactly("boot");
 	}
 
+	@Test
+	@Deprecated
+	public void basicAuthorizationShouldApply() {
+		RestTemplate template = this.builder.basicAuthorization("spring", "boot").build();
+		ClientHttpRequestInterceptor interceptor = template.getInterceptors().get(0);
+		assertThat(interceptor).isInstanceOf(BasicAuthenticationInterceptor.class);
+		assertThat(interceptor).extracting("username").containsExactly("spring");
+		assertThat(interceptor).extracting("password").containsExactly("boot");
+	}
+
 	@Test
 	public void customizersWhenCustomizersAreNullShouldThrowException() {
 		assertThatIllegalArgumentException()