Fix webapp deploy workflow errors and warnings

[jattasNI]

Rationale

I was seeing a couple issues with the new webapp deploy workflows:

1. errors accessing repo variables that specify environment and credentials
   • the workflow was attempting to access some variables as secrets
2. apps being deployed to BYU2026 workspace which most people don't have access to
   • updated to deploy to the Default workspace
3. deprecation warnings about old versions of workflow steps
   • updated versions to latest of workflows reporting warnings

I tested the changes by temporarily updating the workflow to deploy from this branch and verified that the webapps deploy to the correct workspace with no errors or warnings.