Fix for Websocket client upgrade failure

[agnosticdev]

Motivation:

Fix for issue-2631

Modifications:

Make sure the completion handler is sent in the upgrade failure path. Either in the expected or non-expected case.

Result:

Fix for both cases described in the issue.

[agnosticdev]

Rebased main to try to fix API Breakage check.

[adam-fowler]

It appears to have fixed the issue I was having in hummingbird-websocket. But yeah a local test would be a good idea.

[agnosticdev]

Added a unit test for this fix that validates that even if the update path did not succeed notUpgradingCompletionHandler should still be called.