Use proper AssumptionViolatedException

src/tests/junit/org/apache/tools/ant/taskdefs/ExecuteWatchdogTest.java

@@ -25,7 +25,7 @@ import java.util.stream.Collectors;
 import org.apache.tools.ant.util.JavaEnvUtils;
 import org.junit.Before;
 import org.junit.Test;
-import org.junit.internal.AssumptionViolatedException;
+import org.junit.AssumptionViolatedException;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;

src/tests/junit/org/apache/tools/ant/taskdefs/JavaTest.java

@@ -37,7 +37,7 @@ import org.apache.tools.ant.util.TeeOutputStream;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
-import org.junit.internal.AssumptionViolatedException;
+import org.junit.AssumptionViolatedException;
 import org.junit.rules.ExpectedException;
 
 import static org.hamcrest.Matchers.containsString;

src/tests/junit/org/apache/tools/ant/taskdefs/TestProcess.java

@@ -18,7 +18,7 @@
 
 package org.apache.tools.ant.taskdefs;
 
-import org.junit.internal.AssumptionViolatedException;
+import org.junit.AssumptionViolatedException;
 
 /**
  * Interactive Testcase for Processdestroyer.

src/tests/junit/org/apache/tools/mail/MailMessageTest.java

@@ -36,7 +36,7 @@ import java.util.Vector;
 import org.apache.tools.ant.BuildException;
 import org.junit.Before;
 import org.junit.Test;
-import org.junit.internal.AssumptionViolatedException;
+import org.junit.AssumptionViolatedException;
 
 /**
  * JUnit testcases for org.apache.tools.mail.MailMessage.