fix: restore fine-grained token usage in API call

The previous pull reverted the API call to use GITHUB_TOKEN instead of
the provided fine-grained token. Restore the --header Authorization
parameter to use the fine-grained token for organization membership checking.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: sfreudenthaler

.github/actions/security/org-membership-check/action.yml

@@ -46,7 +46,8 @@ runs:
         # This approach correctly handles both public and private organization members
         # without needing to distinguish between their visibility settings.
 
-        response=$(gh api orgs/dotCMS/members/${{ inputs.username }} 2>/dev/null)
+        response=$(gh api orgs/dotCMS/members/${{ inputs.username }} \
+          --header "Authorization: token ${{ inputs.github_token }}" 2>/dev/null)
         api_exit_code=$?
 
         if [ $api_exit_code -eq 0 ]; then