FastGPT: Untrusted PR artifacts are pushed and deployed by privileged preview workflows

FastGPT is a knowledge-based AI application platform. At commit 22ebfacbb43311e9b73294040ae0eb87390c6bba and earlier, artifacts built from untrusted pull request code in .github/workflows/preview-docs-build.yml and .github/workflows/preview-fastgpt-build.yml can be downloaded by privileged workflow_run jobs in .github/workflows/preview-docs-push.yml and .github/workflows/preview-fastgpt-push.yml, allowing attacker-controlled Docker images from the document/ tree or FastGPT build context to be pushed to GHCR and, for documentation previews, deployed with secrets.KUBE_CONFIG_CN.