Update makefile.yml

One more conditional-on-PR-step

Author: jpolitz

.github/workflows/makefile.yml

@@ -120,3 +120,4 @@ jobs:
       run: |
         aws s3 sync ./build/web/js s3://pyret-horizon/horizon-action-test --acl public-read --exclude "*" --include "cpo-main.jarr.gz.js" --content-encoding gzip
         aws s3 sync ./build/web/js s3://pyret-horizon/horizon-action-test --acl public-read --exclude "cpo-main.jarr.js.gz"
+      if: github.event_name != 'pull_request'