Annotate nullability in org.junit.jupiter.engine

Author: marcphilipp

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/package-info.java

@@ -2,4 +2,7 @@
  * Core package for the JUnit Jupiter test engine.
  */
 
+@NullMarked
 package org.junit.jupiter.engine;
+
+import org.jspecify.annotations.NullMarked;