spindle/models: use full at-uri for `TANGLED_PIPELINE_ID`

rkey itself isn't unique across the network because multiple different
knots can emit same rkey. We should use full at-uri here instead.

Signed-off-by: Seongmin Lee <[e-mail]>

spindle/models/pipeline_env.go

···
 	// Standard CI environment variable
 	env["CI"] = "true"
 
-	env["TANGLED_PIPELINE_ID"] = pipelineId.Rkey
+	env["TANGLED_PIPELINE_ID"] = pipelineId.AtUri().String()
 
 	// Repo info
 	if tr.Repo != nil {