Fix release build: pull the image before tagging

The image has to be pulled before it can be tagged.

Author: Aaron Kemp

cloudbuild_release.yaml

@@ -17,6 +17,12 @@
 # (gcp-variant-transforms).
 
 steps:
+  - name: 'gcr.io/cloud-builders/docker'
+    args:
+      - 'pull'
+      - 'gcr.io/${PROJECT_ID}/gcp-variant-transforms:${COMMIT_SHA}'
+    id: 'pull-image'
+
   - name: 'gcr.io/cloud-builders/docker'
     args:
       - 'tag'