Fix executor image release: use correct IMAGE_NAME
Created by: mrnugget
Should fix the build failing: https://buildkite.com/sourcegraph/sourcegraph/builds/109262#73250311-5b8b-424b-a47d-eb3c272d5b5e
Created by: mrnugget
Should fix the build failing: https://buildkite.com/sourcegraph/sourcegraph/builds/109262#73250311-5b8b-424b-a47d-eb3c272d5b5e