Fix `DownloadState.get_ratio()` #3066

Job	Run time
gatekeeper	4s
changes	2s
env	1s
mac	0s
windows	0s
ubuntu	0s
documentation	0s
application_tester	0s
guitest	0s
pytest	0s
scripttest_draft / run	1m 4s
application_tester_draft / run (ubuntu-latest)	4m 7s
guitest_draft / run (windows-latest)	1m 44s
coverage_draft / generate and upload	3m 57s
	10m 59s

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