Modernize rcd_image_version retrieval

[gjtorikian]

GitHub is deprecating the use of set-output, so this PR removes the warning by updating the same logic to the new sequence.

[flavorjones]

Hi, I had tried this over the weekend and I believe it won't work because you can't use env in the container.image portion of the job config. I'll click "approve and run" and we'll see?

[flavorjones]

From the environment files docs

You can make an environment variable available to any subsequent steps in a workflow job by defining or updating the environment variable and writing this to the GITHUB_ENV environment file.

[gjtorikian]

Oh, strange. I'm not sure what you tried but I ported these exact changes into my own builds and it works.

[flavorjones]

Interesting! So if you avoid the ::set-output and use the $GITHUB_ENV file ... you can still use the needs object? 🤯

This PR has some other errors in it, but I'll quickly try another PR and co-author the commit with you!

[flavorjones]

OK, pushed a fixed commit and it seems to be running! 🤞

[flavorjones]

All green! Going to merge. Thank you for showing me how to do this!!

[gjtorikian]

Thank you for showing me how to test and build native gems! 😅 My wish was to pay that forward.