6 files declare their use of PluginCallerInterface in Backup and Migrate 5.0.x

BackupMigrateInterface.php in src/Core/Main/BackupMigrateInterface.php

BrowserDownloadDestination.php in src/Core/Destination/BrowserDownloadDestination.php

FileDirectorySource.php in src/Core/Source/FileDirectorySource.php

MetadataWriter.php in src/Core/Filter/MetadataWriter.php

MySQLiSource.php in src/Core/Source/MySQLiSource.php

Notify.php in src/Core/Filter/Notify.php