Incorrect set comparison between package names and PURLs in NPM sync logic

This line https://github.com/aboutcode-org/purldb/blob/main/minecode_pipelines/pipes/npm.py#L234
`packages_to_sync = list(set(packages).difference(set(synced_packages)))`

does not work because the the "synced_packages" is a list of PURLs (see https://raw.githubusercontent.com/aboutcode-data/minecode-pipelines-config/refs/heads/main/npm/packages_checkpoint.json) while the "packages" is a list of the package names (see https://github.com/aboutcode-org/purldb/blob/main/minecode_pipelines/miners/npm.py#L129)

In another word, the elements in these two sets never match, so everything between these 2 sets are always different.