[Event Hubs Extensions] Update test timeout (Azure#30850)

The focus of these changes is to shift to using the test execution timeout
defined in the test environment for extensions tests.  There has been a
high amount of failures in nightly runs due to hitting the custom short timeout.

Author: jsquire

sdk/eventhub/Microsoft.Azure.WebJobs.Extensions.EventHubs/tests/WebJobsEventHubTestBase.cs

@@ -16,7 +16,7 @@ namespace Microsoft.Azure.WebJobs.Host.EndToEndTests
     public class WebJobsEventHubTestBase
     {
         protected const string TestHubName = "%webjobstesthub%";
-        protected static readonly int Timeout = (int)TimeSpan.FromSeconds(90).TotalMilliseconds;
+        protected static readonly int Timeout = (int)EventHubsTestEnvironment.Instance.TestExecutionTimeLimit.TotalMilliseconds;
 
         /// <summary>The active Event Hub resource scope for the test fixture.</summary>
         protected EventHubScope _eventHubScope;