Fix error path through test.

In a downstream flake I saw this error:
```
timeout_test.go:234: Error waiting for TaskRun pipeline-task-timeout-hdwboxrg-pipelinetask1-2tqsx to be running: %!s(<nil>)
```

This fixes the format string, and corrects what is likely a bug where `err` isn't properly set when printed.

Author: mattmoor

test/timeout_test.go

@@ -107,8 +107,8 @@ func TestPipelineRunTimeout(t *testing.T) {
 	}
 
 	for i := 1; i <= len(taskrunList.Items); i++ {
-		if <-errChan != nil {
-			t.Errorf("Error waiting for TaskRun %s to be running: %s", taskrunList.Items[i-1].Name, err)
+		if err := <-errChan; err != nil {
+			t.Errorf("Error waiting for TaskRun %s to be running: %v", taskrunList.Items[i-1].Name, err)
 		}
 	}
 

test/v1alpha1/timeout_test.go

@@ -230,8 +230,8 @@ func TestPipelineTaskTimeout(t *testing.T) {
 	}
 
 	for i := 1; i <= len(taskrunList.Items); i++ {
-		if <-errChan != nil {
-			t.Errorf("Error waiting for TaskRun %s to be running: %s", taskrunList.Items[i-1].Name, err)
+		if err := <-errChan; err != nil {
+			t.Errorf("Error waiting for TaskRun %s to be running: %v", taskrunList.Items[i-1].Name, err)
 		}
 	}