docs: Updates query to query and wait in samples/desktopapp/user_credentials.py

[DevStephanie]

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Fixes #<issue_number_goes_here> 🦕

[kiraksi]

Looks like you forgot to remove query_job.result() here as I believe query_and_wait returns the result itself, as the cause of your sample errors. Also Tim mentioned in my PR that he wanted to query_job to be renamed to result as well which may also be helpful to you here!

[tswast]

Thanks!