Disable extension uploading to S3 (#4751)

## Problem
We're going to reset S3 buckets for extensions
(https://github.com/neondatabase/aws/pull/413), and as soon as we're
going to change the format we store extensions on S3. Let's stop
uploading extensions in the old format.

## Summary of changes
- Disable `aws s3 cp` step for extensions

.github/workflows/build_and_test.yml

@@ -1007,6 +1007,8 @@ jobs:
           done
 
       - name: Upload postgres-extensions to S3
+        # TODO: Reenable step after switching to the new extensions format (tar-gzipped + index.json)
+        if: false
         run: |
           for BUCKET in $(echo ${S3_BUCKETS}); do
             aws s3 cp --recursive --only-show-errors ./extensions-to-upload s3://${BUCKET}/${{ needs.tag.outputs.build-tag }}/${{ matrix.version }}