Fix the CLI author type to work with CLI 1.22

[offbyone]

This resolves:

../../.asdf/installs/golang/1.20.6/packages/pkg/mod/github.com/hasit/bolter@v0.0.0-20230502180907-68d80baa7620/bolter.go:45:16: cannot use []*cli.Author{…} (value of type []*cli.Author) as []cli.Author value in assignment

[GwynethLlewelyn]

See also #31 — essentially the same, but using urfave/cli/v3 instead. The syntax changed a bit, but at least this should be a bit more future-proof!