Fix testConcurrentSnapshotDeleteAndDeleteIndex (#61228) (#61249)

There is a corner case here in which during partial snapshot the index is
deleted right between starting the snapshot in the CS and the data node getting to work
on it, causing the data node the fail that shard snapshot and making the snapshot `PARTIAL`.

Closes #61208

server/src/test/java/org/elasticsearch/snapshots/SnapshotResiliencyTests.java

@@ -779,8 +779,8 @@ public void onFailure(Exception e) {
         assertThat(snapshotIds, hasSize(1));
 
         final SnapshotInfo snapshotInfo = repository.getSnapshotInfo(snapshotIds.iterator().next());
-        assertEquals(SnapshotState.SUCCESS, snapshotInfo.state());
         if (partialSnapshot) {
+            assertThat(snapshotInfo.state(), either(is(SnapshotState.SUCCESS)).or(is(SnapshotState.PARTIAL)));
             // Single shard for each index so we either get all indices or all except for the deleted index
             assertThat(snapshotInfo.successfulShards(), either(is(indices + 1)).or(is(indices)));
             if (snapshotInfo.successfulShards() == indices + 1) {
@@ -790,6 +790,7 @@ public void onFailure(Exception e) {
                 assertEquals(indexMetadata.getIndex(), firstIndex.get());
             }
         } else {
+            assertEquals(snapshotInfo.state(), SnapshotState.SUCCESS);
             // Index delete must be blocked for non-partial snapshots and we get a snapshot for every index
             assertEquals(snapshotInfo.successfulShards(), indices + 1);
         }