Use stable 8.2 docker image

[Iandenh]

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

I saw that the Dockerfile for 8.2 was using the RC image. I changed that up.
And if I edit the GitHub action file correctly, it should now be required to pass. I haven't done much with GitHub action, so let me know if something is wrong.

[icanhazstring]

Thanks for the improvement 💪