fix: docker-publish build test missing key error (#2623)
The docker-publish github actions workflow builds amd and arm images of
the repository and tests them before publishing. These tests have been
failing since [this
commit](https://github.com/Unstructured-IO/unstructured/commit/ee8b0f93dcba5adb2e4e032346fbaafbe0f45e54)
with an error `UNS_API_KEY environment variable not set`.
The issue is that [this
line](https://github.com/Unstructured-IO/unstructured/blob/b27ad9b6aa4cb29d5d3194cb1f1a0bf1fbaab30b/.github/workflows/docker-publish.yml#L62)
in the workflow is actually blowing away the value assigned to the file
in the previous line
## Changes
* Update line that was overwriting the assignment of UNS_API_KEY to the
uns_test_env_file in the docker-publish workflow to leverage the `>>`
operator so that UNSTRUCTURED_HF_TOKEN assignment is only appended.
* [bonus]: arithmetic expansion in version-sync.sh to keep shell-check
happy
## Testing
To validate, I edited the docker-publish workflow to trigger on push
(and to run the test but not publish the workflow) in [this
commit](https://github.com/Unstructured-IO/unstructured/pull/2623/commits/0f04f5f0f7912853822239d2c0ba43608e71509a).
The successful test results can be reviewed
[here](https://github.com/Unstructured-IO/unstructured/actions/runs/8199826803).
