Update Rust in builder to 1.69.0

For the Sequoia work, we're planning to use 1.69.0 so we need to update
the builder to match. This is being done separately since it already
affects a production component (the cryptography wheel) and should be
tested independently.

This also lets us get rid of our index-warming hack since we can use the
new fast sparse protocol instead
(<https://blog.rust-lang.org/2023/03/09/Rust-1.68.0.html#cargos-sparse-protocol>).

Refs #6817.

builder/Dockerfile

@@ -41,7 +41,7 @@ COPY dh-virtualenv.pref /etc/apt/preferences.d/
 
 RUN apt-get update && apt-get install -y dh-virtualenv
 
-ENV RUST_VERSION 1.58.1
+ENV RUST_VERSION 1.69.0
 ENV RUSTUP_VERSION 1.24.3
 ENV RUSTUP_INIT_SHA256 3dc5ef50861ee18657f9db2eeb7392f9c2a6c95c90ab41e45ab4ca71476b4338
 ENV RUSTUP_HOME /opt/rustup
@@ -55,10 +55,8 @@ RUN TMPDIR=`mktemp -d` && cd ${TMPDIR} \
         && ./rustup-init --default-toolchain=${RUST_VERSION} --profile minimal -y \
         && cd && rm -rf ${TMPDIR}
 ENV PATH "$PATH:/opt/cargo/bin/"
-
-# Warm the cargo index ("empty-library" is reserved by the Rust project)
-# see https://github.com/rust-lang/cargo/issues/10319 and https://github.com/rust-lang/cargo/issues/3377
-RUN cargo install empty-library ||:
+# TODO: Remove after we switch to 1.70.0 when it's enabled by default
+ENV CARGO_REGISTRIES_CRATES_IO_PROTOCOL sparse
 
 # Turn the ossec key into a keyring
 COPY OSSEC-ARCHIVE-KEY.asc /tmp/OSSEC-ARCHIVE-KEY.asc