Fix ConcurrentSnapshotsIT.testEquivalentDeletesAreDeduplicated (#59611)

Trying to queue up snapshot deletes by blocking the delete of the latest
index-N doesn't work here. The first delete will block on the delete operation
but only do so after having already written the updated repository data.
Since that repository data will contain no snapshots, the subsequent deletes for
`*` will just fall through and complete instead of queue up.
=> Fixed by simply waiting on all files on master so that we block before updating
the repository data and get to test the queueing of equivalent operations

closes #59608

server/src/internalClusterTest/java/org/elasticsearch/snapshots/ConcurrentSnapshotsIT.java

@@ -929,7 +929,7 @@ public class ConcurrentSnapshotsIT extends AbstractSnapshotIntegTestCase {
         createIndexWithContent("index-test");
         createNSnapshots(repoName, randomIntBetween(1, 5));
 
-        blockMasterFromDeletingIndexNFile(repoName);
+        blockNodeOnAnyFiles(repoName, masterName);
         final int deletes = randomIntBetween(2, 10);
         final List<ActionFuture<AcknowledgedResponse>> deleteResponses = new ArrayList<>(deletes);
         for (int i = 0; i < deletes; ++i) {