fix: add GITHUB_TOKEN for Claude Code action authentication

Added TERRAFORM_AUTOMATION_TOKEN as GITHUB_TOKEN environment variable
to enable GitHub API access for the Claude Code action. This resolves
the "Bad credentials" authentication error.

Follows the same pattern as terraform-aws-ecr repository.

Author: lgallard

.github/workflows/feature-discovery.yml

@@ -75,6 +75,7 @@ jobs:
         uses: anthropics/claude-code-action@beta
         env:
           CLAUDE_TOKEN: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
+          GITHUB_TOKEN: ${{ secrets.TERRAFORM_AUTOMATION_TOKEN }}
         with:
           claude_code_oauth_token: ${{ env.CLAUDE_TOKEN }}
           mode: agent