fixup! fixup! CI: Cache packages

Author: luke-jr

.github/workflows/build.yaml

@@ -66,7 +66,7 @@ jobs:
           case "${{ matrix.os }}" in
             debian:*|ubuntu:*)
               PKG_CACHE_DIR="/var/cache/apt"
-              INSTALL_CMD="apt update && apt install -y"
+              INSTALL_CMD="apt update && apt -o APT::Clean-Installed=0 install -y"
               PACKAGES="git libc6-dev cmake libcurl4-openssl-dev libjansson-dev libsodium-dev pkgconf"
               PACKAGES_API="libmicrohttpd-dev"
               CLEANUP_CACHE_CMD="rm -rfv ${PKG_CACHE_DIR}/archives/{partial,lock}"