Add org.eclipse.tips.tests to SDK test feature

The tests in org.eclipse.tips.tests recently enabled for the Ant-based
build require the test plug-in to be added to the SDK test feature to be
available during the build.

Complements
#1924

eclipse.platform.releng/features/org.eclipse.sdk.tests/feature.xml

@@ -203,6 +203,10 @@
          id="org.eclipse.ui.tests"
          version="0.0.0"/>
 
+   <plugin
+         id="org.eclipse.tips.tests"
+         version="0.0.0"/>
+
    <plugin
          id="org.eclipse.ua.tests"
          version="0.0.0"/>