Skip prereleases for restore bwc tests too

core/src/test/java/org/elasticsearch/bwcompat/RestoreBackwardsCompatIT.java

@@ -96,7 +96,7 @@ public class RestoreBackwardsCompatIT extends AbstractSnapshotIntegTestCase {
         SortedSet<String> expectedVersions = new TreeSet<>();
         for (Version v : VersionUtils.allVersions()) {
             if (VersionUtils.isSnapshot(v)) continue;  // snapshots are unreleased, so there is no backcompat yet
-            if (v.isAlpha()) continue; // no guarantees for alpha releases
+            if (v.isRelease() == false) continue; // no guarantees for prereleases
             if (v.onOrBefore(Version.V_2_0_0_beta1)) continue; // we can only test back one major lucene version
             if (v.equals(Version.CURRENT)) continue; // the current version is always compatible with itself
             expectedVersions.add(v.toString());