base the docker image on distroless trixie

static-debian12 (bookworm) -> static-debian13. Multi-platform builds
(linux/amd64, linux/arm64 -- the latter is what Docker on Apple
silicon runs) were already in place via dockers_v2 platforms.

Refs: #21

Author: xobotyi

Dockerfile

@@ -1,8 +1,8 @@
 # Runtime image for the release pipeline: goreleaser (dockers_v2) lays the
 # prebuilt binaries out per platform in the build context. distroless/static
-# ships CA certificates (required for HTTPS to Gerrit) and runs as a non-root
-# user.
-FROM gcr.io/distroless/static-debian12:nonroot
+# (trixie) ships CA certificates (required for HTTPS to Gerrit) and runs as a
+# non-root user.
+FROM gcr.io/distroless/static-debian13:nonroot
 
 ARG TARGETPLATFORM