pkg_agent() errors in default usecase

```
> beekeeper::generate_pkg()
Error in is_character(x, n = 1L) : 
  promise already under evaluation: recursive default argument reference or earlier problems?
```

vs

```
> agent <- pkg_agent()
> beekeeper::generate_pkg(pkg_agent = agent)
✔ Writing 'R/010-call.R'
```

Something about the checks is causing a conflict. Try to untangle the usethis checks to make this work!