MESSAGEix nightly testing snapshots

These files contain exported MESSAGEix-GLOBIOM scenarios used for testing of message_ix (doi: 10.5281/zenodo.4005684) and validation of changes to its code. They were previously hosted on an IIASA-internal web server at https://data.ene.iiasa.ac.at and fetched from there by code in message_ix.testing.nightly. The current record allows the same data to be accessed through the message_ix_models.model.snapshot features (see the documentation) also used for public snapshots such as doi:10.5281/zenodo.5793869.