Move ExecCompletes_Issue943 to long running

This is 2 of the 6 minutes of test CPU time locally....don't need to hang on this so much.

tests/StackExchange.Redis.Tests/Transactions.cs

@@ -1206,7 +1206,7 @@ public async Task WatchAbort_HashLengthEqual()
         }
 #endif
 
-        [Fact]
+        [FactLongRunning]
         public async Task ExecCompletes_Issue943()
         {
             int hashHit = 0, hashMiss = 0, expireHit = 0, expireMiss = 0;