chore: use multiplatform shas for images

docker buildx imagetools inspect <image> will show the overall
manifest sha unlike docker hub which only shows shas for specific
platforms.

Dockerfile

@@ -1,6 +1,6 @@
 # Leveraging the pre-built Docker images with
 # cargo-chef and the Rust toolchain
-FROM lukemathwalker/cargo-chef:latest-rust-1.74-bookworm AS chef
+FROM lukemathwalker/cargo-chef:latest-rust-1.74-bookworm@sha256:f2be0d7e17e30166653ccc67498e82759d8124ed8770b48f06395caa8e95c97f AS chef
 WORKDIR app
 
 FROM chef AS planner
@@ -16,7 +16,7 @@ COPY . .
 RUN cargo build --release --bin sinker
 
 # We do not need the Rust toolchain to run the binary!
-FROM debian:bookworm-slim
+FROM debian:bookworm-slim@sha256:f80c45482c8d147da87613cb6878a7238b8642bcc24fc11bad78c7bec726f340
 
 RUN apt update \
     && apt install --yes ca-certificates libssl3 --no-install-recommends \