OWImportDocuments: plural fix #1340

Job	Run time
test / build (macOS-latest, 3.10, orange-released, 5.15., false) / orange-released macOS-latest py3.10 qt5.15.	5m 29s
test / build (macOS-latest, 3.9, orange-oldest, 5.15., false) / orange-oldest macOS-latest py3.9 qt5.15.	5m 58s
test / build (macOS-latest, 3.11, orange-latest, 5.15., false) / orange-latest macOS-latest py3.11 qt5.15.	7m 35s
test / build (macOS-latest, 3.10, orange-released, 6.6., false) / orange-released macOS-latest py3.10 qt6.6.	6m 10s
test / build (ubuntu-latest, 3.10, orange-released, 6.6., false) / orange-released ubuntu-latest py3.10 qt6.6.	5m 9s
test / build (ubuntu-latest, 3.10, orange-released, 5.15., false) / orange-released ubuntu-latest py3.10 qt5.15.	5m 4s
test / build (ubuntu-latest, 3.11, orange-latest, 5.15., false) / orange-latest ubuntu-latest py3.11 qt5.15.	7m 37s
test / build (ubuntu-latest, 3.9, orange-oldest, 5.15., false) / orange-oldest ubuntu-latest py3.9 qt5.15.	5m 5s
test / build (windows-latest, 3.10, orange-released, 6.6., false) / orange-released windows-latest py3.10 qt6.6.	6m 40s
test / build (windows-latest, 3.10, orange-released, 5.15., false) / orange-released windows-latest py3.10 qt5.15.	6m 2s
test / build (windows-latest, 3.11, orange-latest, 5.15., false) / orange-latest windows-latest py3.11 qt5.15.	8m 24s
test / build (windows-latest, 3.9, orange-oldest, 5.15., false) / orange-oldest windows-latest py3.9 qt5.15.	5m 48s
	1h 15m 1s

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