Pins the remaining tag- and branch-referenced GitHub Actions and the
`postgres` service image to specific commit SHAs / digests, so workflow
runs resolve to fixed versions. Edited in the xtask workflow DSL and
regenerated with `cargo xtask workflows`.
- `bufbuild/buf-setup-action` → `a47c93e0` (v1.50.0)
- `bufbuild/buf-breaking-action` → `c57b3d84` (v1.1.4)
- `digitalocean/action-doctl` → `3cb39531` (v2.5.2)
- `postgres:15` → `@sha256:1b92e7a8…`
- `deploy_docs.yml` reusable workflow → pinned to a commit
Release Notes:
- N/A