Invalid Sink URI CloudEvent test sometimes includes quotes

In the logs for the latest pipeline nightly we saw a failed unit test
for CloudEvents with the following message:

```
TestSendCloudEvent/send_a_cloud_event_with_invalid_sink_URI:
cloudevent_test.go:106: I expected an error like invalid_URI:
unsupported protocol scheme, but I got Post "invalid_URI": unsupported
protocol scheme ""
```

It appears that sometimes the "invalid_URI" part of the error message
will include quotes, and sometimes (like when running locally) it won't.

This PR updates the regex to allow for these quotes in the error message.

pkg/reconciler/taskrun/resources/cloudevent/cloudevent_test.go

@@ -73,7 +73,7 @@ func TestSendCloudEvent(t *testing.T) {
 		eventSourceURI:   defaultEventSourceURI,
 		cloudEventClient: defaultCloudEventClient,
 		wantErr:          true,
-		errRegexp:        fmt.Sprintf("%s: unsupported protocol scheme", invalidSinkURI),
+		errRegexp:        fmt.Sprintf("\"?%s\"?: unsupported protocol scheme", invalidSinkURI),
 	}, {
 		desc:             "send a cloud event, fail to send",
 		sinkURI:          defaultSinkURI,