Fixing context path

[BretFisher]

Fixing a reusable workflow call. The docker build-push-action uses "git context" rather than the typical actions/checkout to clone the repo for building. When a subdir is needed as the build context in this case, the field has a special format:

context: "{{defaultContext}}:subdir"

https://github.com/docker/build-push-action?tab=readme-ov-file#git-context

[github-actions]

Docker image tag(s) pushed:

bretfisher/examplevotingapp_worker:gha-7850539360
bretfisher/examplevotingapp_worker:pr-76
ghcr.io/bretfisher/example-voting-app-worker:gha-7850539360
ghcr.io/bretfisher/example-voting-app-worker:pr-76 

Labels added to images:

org.opencontainers.image.created=2024-02-09T22:57:27.827Z
org.opencontainers.image.description=Example Docker Compose app
org.opencontainers.image.licenses=Apache-2.0
org.opencontainers.image.revision=ade310f8c2ae78a703db0c3996f1ea8f7c63894c
org.opencontainers.image.source=https://github.com/BretFisher/example-voting-app
org.opencontainers.image.title=example-voting-app
org.opencontainers.image.url=https://github.com/BretFisher/example-voting-app
org.opencontainers.image.version=gha-7850539360

[BretFisher]

I'll fix the npm install fail during result build in a future PR.