TransportBroadcastAction should always set response for each shard (#84926)

The TransportBroadcastAction can leave the responses of some group unset
if all shards of that group hit shard_unavailable_exception.

Author: dnhatn

docs/changelog/84926.yaml

@@ -0,0 +1,5 @@
+pr: 84926
+summary: '`TransportBroadcastAction` should always set response for each shard'
+area: Search
+type: bug
+issues: []

server/src/main/java/org/elasticsearch/action/support/broadcast/TransportBroadcastAction.java

@@ -262,11 +262,6 @@ protected void finishHim() {
         }
 
         void setFailure(ShardIterator shardIt, int shardIndex, Exception e) {
-            // we don't aggregate shard failures on non active shards (but do keep the header counts right)
-            if (TransportActions.isShardNotAvailableException(e)) {
-                return;
-            }
-
             if ((e instanceof BroadcastShardOperationFailedException) == false) {
                 e = new BroadcastShardOperationFailedException(shardIt.shardId(), e);
             }