bug#31302: `guix import json` doesn't handle inputs with the form 'package:output'

[Lulu]

I just checked this and failed to replicate it. It happily generates config from
`glib:doc', `glib:bin' and `glib:out' in input fields and complains if there's a
nonexistent `glib:foo' input, as of v1.1.0.

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Lulu