Adapts to jenkinsci/jenkins#23873 so the tests pass on the current Jenkins version as well as a version containing the PR (#401)

discovered by jenkinsci/bom#6031 in preparation for jenkinsci/jenkins#23873

tested with mvn test -Djenkins.version=2.540-rc37747.87da_150079a_1

Author: jtnord

src/test/java/hudson/tasks/MailerTest.java

@@ -48,6 +48,7 @@
 import org.jenkinsci.plugins.workflow.cps.CpsFlowDefinition;
 import org.jenkinsci.plugins.workflow.job.WorkflowJob;
 import org.jenkinsci.plugins.workflow.job.WorkflowRun;
+import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 import org.jvnet.hudson.test.Email;
 import org.jvnet.hudson.test.FailureBuilder;
@@ -104,6 +105,12 @@ private static Mailbox getMailbox(String recipient) throws Exception {
         return Mailbox.get(new InternetAddress(recipient));
     }
 
+    @BeforeAll
+    static void enableManagePermission() {
+        // TODO remove when baseline contains https://github.com/jenkinsci/jenkins/pull/23873
+        Jenkins.MANAGE.setEnabled(true);
+    }
+
     private static Mailbox getEmptyMailbox(String recipient) throws Exception {
         Mailbox inbox = getMailbox(recipient);
         inbox.clear();
@@ -501,7 +508,7 @@ void doCheckSmtpServerShouldThrowExceptionForUserWithoutManagePermissions(Jenkin
         rule.jenkins.setAuthorizationStrategy(new MockAuthorizationStrategy()
                 .grant(Jenkins.READ).everywhere().to(USER)
         );
-        final String expectedErrorMessage = "user is missing the Overall/Administer permission";
+        final String expectedErrorMessage = "user is missing the Overall/Manage permission";
 
         try (ACLContext ignored = ACL.as(User.getById(USER, true))) {
             RuntimeException runtimeException = assertThrows(RuntimeException.class,