update to only allow prod in the deployment

[louisachu]

Change the prod production to only deploy to prod only.

Related Issue

https://jira.corp.adobe.com/browse/DEVSITE-1674

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[melissag-ensemble]

I think this misses the ticket. DEVSITE-1674 wants prod to stay main-only and not be deployable from non-main branches. (Slack)

Hardcoding env: prod changes behavior in the wrong direction:

Branch	Before (dropdown)	After this PR
main	can deploy prod or stage & prod	prod only — can no longer do stage & prod together
non-main	could select prod (the bug)	still forces prod — bug not fixed, and no dropdown to avoid it

AdobeDocs/adp-devsite-workflow#44 adds a guard in the central deploy-v2.yml that rejects prod deploys from non-main branches, which fixes this for every content repo without removing the dropdown options. I think we can close this one in favor of that. What do you think?