Add nullability annotations to tests in system-test/spring-boot-image-system-test

See gh-47263

system-test/spring-boot-image-system-tests/build.gradle

@@ -62,3 +62,11 @@ dependencies {
 toolchain {
 	maximumCompatibleJavaVersion = JavaLanguageVersion.of(23)
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}
+
+tasks.named("compileSystemTestJava") {
+	options.nullability.checking = "tests"
+}