Resolve release reploy action warnings

[jeffpaul]

Is your enhancement related to a problem? Please describe.

As part of the 1.6.0 release GitHub Action deploy to WordPress.org there were 3 warnings that we might look to resolve so future releases run more smoothly:

• The following actions uses node12 which is deprecated and will be forced to run on node16: actions/upload-release-asset@v1.0.2. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/
• The following actions use a deprecated Node.js version and will be forced to run on node20: actions/upload-release-asset@v1.0.2. For more info: https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/
• The set-output command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

So we'll likely want to update https://github.com/mailchimp/wordpress/blob/develop/.github/workflows/wordpress-plugin-deploy.yml to:

• replace https://github.com/actions/upload-release-asset with https://github.com/softprops/action-gh-release?tab=readme-ov-file#%EF%B8%8F-uploading-release-assets << this should resolve issues 1 & 2 above
• uncertain if the above will resolve issue 3 as well, so if not we'll want to investigate where set-output is coming in from (though I think that's from the deprecated action utilized above)

Designs

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Describe alternatives you've considered

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