Correct input to the peter-evans/dockerhub-description Action

[mcdonnnj]

🗣 Description

This pull request fixes an input to the peter-evans/dockerhub-description Action to be one that actually exists.

💭 Motivation and context

I'm not sure what I was doing in #213 but I used an input that doesn't exist for the Action. When that PR was merged I checked to verify the the step using this Action was run and saw the ominous Warning: Unexpected input(s) 'description', valid inputs are ['username', 'password', 'repository', 'short-description', 'readme-filepath', 'enable-url-completion', 'image-extensions'].

🧪 Testing

Automated tests pass. I verified that all inputs actually exist for the Action in question.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All new and existing tests pass.