[Templating][Fixes #15048] Fixes build hang in template tests caused by an unbound blocking collection

[javiercn]

There is an underlying issue here, which is a race condition between console logging and hosting logging.

In some rare cases the messages on the console for both get interleaved in wrong ways like dbugNow listening on: http://127.0.0.1:12857 which causes the test to fail finding the Listening on: pattern.

• It prevents waiting indefinitely on the blocked collection, which is what caused the hangs.
• It relaxes the pattern we use to find the message so that it can match simpler values and accounts for the message being preceded by other text in the output as in the example above.

Filed #15060 to triage the underlying hosting issue.