fix the test by setting the indexer flag

Author: vladak

opengrok-indexer/src/test/java/org/opengrok/indexer/history/FileHistoryCacheTest.java

@@ -860,6 +860,7 @@ void testNoHistoryFetch() throws Exception {
         env.setFetchHistoryWhenNotInCache(false);
 
         // Pretend we are done with first phase of indexing.
+        env.setIndexer(true);
         HistoryGuru.getInstance().setHistoryIndexDone();
 
         // First try repo with ability to fetch history for directories.