Skip specific test for NATS servers earlier than v2.10

This commit updates the KeyValueStoreTest to skip the Test_CombinedSources test for NATS server versions earlier than 2.10 since some of the mirroring features are introduced with 2.10. It also removes unnecessary retry delay and timeout parameters from the test configuration.

tests/NATS.Client.KeyValueStore.Tests/KeyValueStoreTest.cs

@@ -649,7 +649,7 @@ public async Task TestDirectMessageRepublishedSubject()
         Assert.Equal("tres", kve3.Value);
     }
 
-    [Fact]
+    [SkipIfNatsServer(versionEarlierThan: "2.10")]
     public async Task Test_CombinedSources()
     {
         await using var server = NatsServer.StartJS();
@@ -687,9 +687,7 @@ await Retry.Until(
                 }
 
                 return true;
-            },
-            retryDelay: TimeSpan.FromSeconds(3),
-            timeout: TimeSpan.FromSeconds(30));
+            });
 
         var entryA = await storeCombined.GetEntryAsync<string>("ss1_a");
         var entryB = await storeCombined.GetEntryAsync<string>("ss2_b");