Update validation scripts for Bicep extension installation

[jasonviviano]

Overview of feature request

Update the Bicep extension validation script

Acceptance criteria

GHCR is used for the pull command, example:
https://github.com/radius-project/radius/pull/7293/files

Additional context

Found here:

recipes/.github/workflows/validate-bicep.yaml

Line 44 in 17f2799

         ./.github/scripts/curl-with-retries.sh https://get.radapp.dev/tools/bicep-extensibility/${{ env.REL_CHANNEL }}/linux-x64/rad-bicep --output rad-bicep 

AB#12069