build: pin versions for docker base images

>  2 warnings found (use --debug to expand):
> - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 6)
> - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line
11)

Dockerfile

@@ -1,14 +1,14 @@
 # Leveraging the pre-built Docker images with
 # cargo-chef and the Rust toolchain
-FROM git.kemitix.net/kemitix/git-next-builder:latest AS chef
+FROM git.kemitix.net/kemitix/git-next-builder:2024.07.05 AS chef
 WORKDIR /app
 
-FROM chef as planner
+FROM chef AS planner
 COPY Cargo.toml ./
 COPY crates crates
 RUN cargo chef prepare --recipe-path recipe.json
 
-FROM chef as builder
+FROM chef AS builder
 COPY --from=planner /app/recipe.json recipe.json
 RUN cargo chef cook --profile release --recipe-path recipe.json
 COPY . .

Dockerfile.builder

@@ -1,4 +1,4 @@
-FROM docker.io/rust:latest
+FROM docker.io/rust:1.79.0-bookworm
 
 RUN apt-get update && \
   apt-get install -y clang-16 mold && \