Translation test for currently open document does not always start

Steps to reproduce:

• Open attached project
• Import attached translations.json from Translations view -> Import translations
• Click "Run translation test for the currently open document.." button
• Translation test is not started, Translation tester dialog stays open
  
• After trying multiple times, closing project and opening it again, running "Generate Qt translation source files" first I might get the translation test working
• Issue also in running test for the whole project, reported in separate issue https://bugreports.qt.io/browse/QDS-12461