Fix archive content hash computation for model publication

For some reason, some files are not used to compute the hash of the model archive. The bug was noticed while publishing a pylaia model whose weights.ckpt was modified.

The bug seems to come from https://gitlab.com/teklia/arkindex/cli/-/blob/master/arkindex_cli/commands/models/utils.py#L95

[os.path.isfile()](https://docs.python.org/3/library/os.path.html#os.path.isfile) seems to have issues when lacking permissions just like os.path.exists.