tools/flow: avoid looking like we're using go run for real

While grepping around to replace `go run cuelang.org/go/cmd/cue`
with `go tool cue`, I had to do a double take before I realised
that this file was not actually running the cue tool at all.
Make that more obvious, which doesn't alter the test behavior.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I378a810eb0db62e46c55a6ea00483ae42ed6c70a
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1218732
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>

Author: mvdan

tools/flow/testdata/template.txtar

@@ -20,7 +20,7 @@ root: {
 	}
 	convert: exec.Run & {
 		stdin: get.response.body
-		cmd:   "go run cuelang.org/go/cmd/cue import -f -p json -l #Workflow: jsonschema: - --outfile pkg/github.com/SchemaStore/schemastore/src/schemas/json/github-workflow.cue"
+		cmd:   "cue-fake import -f -p json -l #Workflow: jsonschema: - --outfile pkg/github.com/SchemaStore/schemastore/src/schemas/json/github-workflow.cue"
 	}
 }
 -- out/run/errors --
@@ -65,7 +65,7 @@ graph TD
 -- out/run/t2/value --
 {
 	$id: "tool/exec.Run"
-	cmd: "go run cuelang.org/go/cmd/cue import -f -p json -l #Workflow: jsonschema: - --outfile pkg/github.com/SchemaStore/schemastore/src/schemas/json/github-workflow.cue"
+	cmd: "cue-fake import -f -p json -l #Workflow: jsonschema: - --outfile pkg/github.com/SchemaStore/schemastore/src/schemas/json/github-workflow.cue"
 	env: {} | []
 	stderr:      null
 	stdin:       GET.response.body & (*null | string | bytes)
@@ -120,7 +120,7 @@ graph TD
 -- out/run/t3/value --
 {
 	$id: "tool/exec.Run"
-	cmd: "go run cuelang.org/go/cmd/cue import -f -p json -l #Workflow: jsonschema: - --outfile pkg/github.com/SchemaStore/schemastore/src/schemas/json/github-workflow.cue"
+	cmd: "cue-fake import -f -p json -l #Workflow: jsonschema: - --outfile pkg/github.com/SchemaStore/schemastore/src/schemas/json/github-workflow.cue"
 	env: {}
 	stdout:  "foo"
 	stderr:  null