[TEST] ignore transient error in overlapping downsample (#108001)

* Add retries in concurrent downsampling action

* [TEST] ignore transient error in overlapping downsample

x-pack/plugin/downsample/src/test/java/org/elasticsearch/xpack/downsample/DownsampleActionSingleNodeTests.java

@@ -555,8 +555,13 @@ public void onFailure(Exception e) {
             }
         });
 
-        // Downsample with retries, in case the downsampled index is not ready.
-        assertBusy(() -> downsample(sourceIndex, downsampleIndex, config), 120, TimeUnit.SECONDS);
+        assertBusy(() -> {
+            try {
+                client().execute(DownsampleAction.INSTANCE, new DownsampleAction.Request(sourceIndex, downsampleIndex, TIMEOUT, config));
+            } catch (ElasticsearchException e) {
+                fail("transient failure due to overlapping downsample operations");
+            }
+        });
 
         // We must wait until the in-progress downsample ends, otherwise data will not be cleaned up
         assertBusy(() -> assertTrue("In progress downsample did not complete", downsampleListener.success), 60, TimeUnit.SECONDS);