prevent php8 warnings, fixes #3106

app/controllers/course/contentmodules.php

app/controllers/course/elearning.php

app/controllers/course/wizard.php

app/controllers/new_password.php

app/controllers/resources/room_request.php

app/views/course/contentmodules/info.php

lib/classes/coursewizardsteps/BasicDataWizardStep.php

lib/elearning/ELearningUtils.class.php

lib/filesystem/PublicFolder.php

lib/models/Course.class.php

lib/models/OERMaterial.php

lib/models/SimpleCollection.class.php

lib/plugins/core/CorePlugin.php

lib/plugins/core/StudIPPlugin.class.php

lib/plugins/engine/PluginManager.class.php

lib/visual.inc.php