Use the right version of bicep using oras in workflow (#7293)

# Description

This is to use bicep binary from ghcr because
`https://get.radapp.dev/tools/bicep-extensibility` is not used anymore.

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Fixes: #issue_number

Signed-off-by: Young Bu Park <[email protected]>

.github/workflows/validate-bicep.yaml

@@ -35,9 +35,10 @@ jobs:
         uses: actions/checkout@v3
       - name: Parse release version and set environment variables
         run: python ./.github/scripts/get_release_version.py
+      - uses: oras-project/setup-oras@v1
       - name: Download rad-bicep
         run: |
-          ./.github/scripts/curl-with-retries.sh https://get.radapp.dev/tools/bicep-extensibility/${{ env.REL_CHANNEL }}/linux-x64/rad-bicep --output rad-bicep
+          oras pull ghcr.io/radius-project/radius/bicep/rad-bicep/linux-x64:latest -o ./
           chmod +x rad-bicep
           ./rad-bicep --version
       - name: Verify Bicep files