Make DenseConjunctionBulkScorer set a Scorer.

This is important because some composite scorers collect the same
segment with different scorers. So if a `BulkScorer` doesn't set a
`Scorer`, the collector may implicitly use the scorer that was used to
collect a previous window of doc IDs.

Closes #14088.

lucene/core/src/java/org/apache/lucene/search/DenseConjunctionBulkScorer.java

@@ -69,6 +69,9 @@ public int score(LeafCollector collector, Bits acceptDocs, int min, int max) thr
       return lead.docID();
     }
 
+    // This scorer is only used for conjunctions of FILTER clauses, so we set a simple scorer that
+    // always returns a score of zero.
+    collector.setScorer(new SimpleScorable());
     List<DocIdSetIterator> otherIterators = this.others;
     DocIdSetIterator collectorIterator = collector.competitiveIterator();
     if (collectorIterator != null) {