Use jdk11 primitives in test to allow backport to branch_9x (#13311)

diff --git a/lucene/core/src/test/org/apache/lucene/search/BaseKnnVectorQueryTestCase.java b/lucene/core/src/test/org/apache/lucene/search/BaseKnnVectorQueryTestCase.java
index 2ae0ae1..2546115 100644
--- a/lucene/core/src/test/org/apache/lucene/search/BaseKnnVectorQueryTestCase.java
+++ b/lucene/core/src/test/org/apache/lucene/search/BaseKnnVectorQueryTestCase.java
@@ -781,7 +781,7 @@
       TimeLimitingKnnCollectorManager noTimeoutManager =
           new TimeLimitingKnnCollectorManager(delegate, null);
       KnnCollector noTimeoutCollector =
-          noTimeoutManager.newCollector(Integer.MAX_VALUE, searcher.leafContexts.getFirst());
+          noTimeoutManager.newCollector(Integer.MAX_VALUE, searcher.leafContexts.get(0));
 
       // Check that a normal collector is created without timeout
       assertTrue(noTimeoutCollector instanceof TopKnnCollector);
@@ -797,7 +797,7 @@
       TimeLimitingKnnCollectorManager timeoutManager =
           new TimeLimitingKnnCollectorManager(delegate, () -> true);
       KnnCollector timeoutCollector =
-          timeoutManager.newCollector(Integer.MAX_VALUE, searcher.leafContexts.getFirst());
+          timeoutManager.newCollector(Integer.MAX_VALUE, searcher.leafContexts.get(0));
 
       // Check that a time limiting collector is created, which returns partial results
       assertFalse(timeoutCollector instanceof TopKnnCollector);