Change concurrency group

[scottyhq]

using a static name was causing PRs and main branch merges to cancel each other, might be better to simply have separate 'test' and 'deploy' workflows

https://docs.github.com/en/actions/using-jobs/using-concurrency#example-only-cancel-in-progress-jobs-or-runs-for-the-current-workflow

[github-actions[bot]]

🎊 PR Preview 84b979a1681aae4a777984267187b650281f5208 has been successfully built and deployed to https://xarray-contrib-xarray-tutorial-preview-pr-209.surge.sh

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