evaluator: non-package CUE fails to complain about superfluous import

[myitcv]

What version of CUE are you using (cue version)?

$ cue version
cue version v0.0.0-20220808083940-b4d1b16ccf89

       -compiler gc
     CGO_ENABLED 1
          GOARCH arm64
            GOOS linux
             vcs git
    vcs.revision b4d1b16ccf8944599eec6870da400d2b56da979b
        vcs.time 2022-08-08T08:39:40Z
    vcs.modified false

Does this issue reproduce with the latest release?

Yes

What did you do?

! exec cue eval x.cue
cmp stderr stderr.golden

-- x.cue --
import "list"

x: 5
-- stderr.golden --
imported and not used: "list":
    ./x.cue:1:8

What did you expect to see?

Passing test.

What did you see instead?

> ! exec cue eval x.cue
[stdout]
x: 5
FAIL: /tmp/testscript3669738402/repro.txtar/script.txt:1: unexpected command success

If you add a package class to x.cue the cue eval fails as expected (modulo line numbers).

FYI @rogpeppe @mpvl - raising this after we spotted it recently.