During Gnocchi charm upgrade, layer-basic failed to upgrade packages

During a charm upgrade to [gnocchi rev 46](https://charmhub.io/gnocchi), layer-basic somehow failed to recreate its venv and install the new requirements/dependencies defined by the charm. To work around the issue, I deleted the .venv directory and the .bootstapped file from the wheelhouse directory. After doing both, the layer installed the new packages/dependencies correctly.