[TEST] Fix testConcurrentTermIncreaseOnReplicaShard

This test has a bug that got introduced during the refactoring of #32442. With 2 concurrent term increments,
we can only assert under the operation permit that we are in the correct operation term, not that there is
not already another term bump pending.

Closes #34862

Author: ywelsch

server/src/test/java/org/elasticsearch/index/shard/IndexShardTests.java

@@ -1058,7 +1058,7 @@ public void testConcurrentTermIncreaseOnReplicaShard() throws BrokenBarrierExcep
                         @Override
                         public void onResponse(Releasable releasable) {
                             counter.incrementAndGet();
-                            assertThat(indexShard.getPendingPrimaryTerm(), equalTo(primaryTerm + increment));
+                            assertThat(indexShard.getOperationPrimaryTerm(), equalTo(primaryTerm + increment));
                             latch.countDown();
                             releasable.close();
                         }
@@ -1103,6 +1103,7 @@ public void onFailure(Exception e) {
         }
 
         assertThat(indexShard.getPendingPrimaryTerm(), equalTo(primaryTerm + Math.max(firstIncrement, secondIncrement)));
+        assertThat(indexShard.getOperationPrimaryTerm(), equalTo(indexShard.getPendingPrimaryTerm()));
 
         closeShards(indexShard);
     }