Tests: Avoid an infinite loop in `Spy_REST_Server` if a non-existing … #14202

Job	Run time
QUnit Tests	2m 16s
Slack Notifications / Prepare notifications	3s
Slack Notifications / Success notifications	2s
Slack Notifications / Failure notifications	0s
Slack Notifications / Fixed notifications	0s
Slack Notifications / Cancelled notifications	0s
Failed workflow tasks	0s
	2m 21s

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