Create all test results in AzureDevOpsBuild.GetTestRuns before disposing the TestManagementHttpClient

Resolves #251

Author: Christian Bumann

src/Cake.AzureDevOps/Pipelines/AzureDevOpsBuild.cs

@@ -436,7 +436,7 @@ public IEnumerable<AzureDevOpsTestRun> GetTestRuns()
                                     this.GetTestResults(testClient, runId)
                                     .GetAwaiter()
                                     .GetResult(),
-                            });
+                            }).ToList();
             }
         }