cmd/cue: JSONSchema import emits invalid CUE

[jpluscplusm]

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

$ cue version
cue version v0.6.0

go version go1.20.6
      -buildmode exe
       -compiler gc
       -trimpath true
     CGO_ENABLED 0
          GOARCH amd64
            GOOS linux
         GOAMD64 v1

Does this issue reproduce with the latest stable release?

Yes, 0.6.0

What did you do?

exec wget https://raw.githubusercontent.com/buildkite/pipeline-schema/6396f68d5e983e0d2acbf829c565027a4cfd69bc/schema.json
exec cue import schema.json
exec cue vet schema.cue

What did you expect to see?

A passing testscript.

What did you see instead?

> exec wget -q https://raw.githubusercontent.com/buildkite/pipeline-schema/6396f68d5e983e0d2acbf829c565027a4cfd69bc/schema.json
> exec cue import schema.json
> exec cue vet schema.cue
[stderr]
expected selector, found 'if':
    ./schema.cue:31:33
expected selector, found 'if':
    ./schema.cue:53:30
expected selector, found 'if':
    ./schema.cue:98:38
expected selector, found 'if':
    ./schema.cue:141:38
expected selector, found 'if':
    ./schema.cue:148:23
expected selector, found 'if':
    ./schema.cue:155:23
expected selector, found 'if':
    ./schema.cue:162:23
expected selector, found 'if':
    ./schema.cue:229:39
expected selector, found 'if':
    ./schema.cue:279:30
expected selector, found 'if':
    ./schema.cue:300:44
[exit status 1]
FAIL: /tmp/testscript3892460085/broken-if-field.txtar/script.txtar:3: unexpected command failure
error running broken-if-field.txtar in /tmp/testscript3892460085/broken-if-field.txtar

cue import emits CUE which (I believe) doesn't correctly cater for the presence of CUE keywords as fields in the input JSONSchema. Here's an example of the broken output CUE:

	if?:            #commonOptions.if

I'm not sure if it's the LHS or RHS that's the problem.