Null-mark org.springframework.test.web.support package

See gh-36054

spring-test/src/main/java/org/springframework/test/web/support/package-info.java

@@ -1,4 +1,7 @@
 /**
  * Support classes for testing web applications.
  */
+@NullMarked
 package org.springframework.test.web.support;
+
+import org.jspecify.annotations.NullMarked;