CI: Update Dockerfile to install OpenSSL 3

The custom container is no longer required since the upstream image has
removed (the old version of) OpenSSL entirely.

docker/aarch64-unknown-linux-gnu/Dockerfile

@@ -1,8 +1,4 @@
-FROM ghcr.io/tesaguri/cross:aarch64-unknown-linux-gnu
+FROM rustembedded/cross:aarch64-unknown-linux-gnu
 
-RUN dpkg --add-architecture arm64 && \
-    apt-get update && \
-    apt-get install --assume-yes libsqlite3-dev libsqlite3-dev:arm64 libssl-dev:arm64
-
-ENV PKG_CONFIG_ALLOW_CROSS_aarch64_unknown_linux_gnu=1 \
-    PKG_CONFIG_PATH_aarch64_unknown_linux_gnu='/usr/lib/aarch64-linux-gnu/pkgconfig'
+COPY install_packages.sh /
+RUN /install_packages.sh arm64

docker/armv7-unknown-linux-gnueabihf/Dockerfile

@@ -1,8 +1,4 @@
-FROM ghcr.io/tesaguri/cross:armv7-unknown-linux-gnueabihf
+FROM rustembedded/cross:armv7-unknown-linux-gnueabihf
 
-RUN dpkg --add-architecture armhf && \
-    apt-get update && \
-    apt-get install --assume-yes libsqlite3-dev libsqlite3-dev:armhf libssl-dev:armhf
-
-ENV PKG_CONFIG_ALLOW_CROSS_armv7_unknown_linux_gnueabihf=1 \
-    PKG_CONFIG_PATH_armv7_unknown_linux_gnueabihf='/usr/lib/arm-linux-gnueabihf/pkgconfig'
+COPY install_packages.sh /
+RUN /install_packages.sh armhf

docker/install_packages.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+
+set -xeo pipefail
+
+RUN dpkg --add-architecture "$1"
+
+if grep -Eq '^UBUNTU_CODENAME=focal$' /etc/os-release; then
+	# Use `libssl3` package from Ubuntu 22.04 (jammy) since 20.04 (focal) doesn't have the package.
+	# <https://amedee.be/install-libssl3-on-systems-before-jammy/>
+    echo 'APT::Default-Release "focal";' > /etc/apt/apt.conf.d/01ubuntu
+	awk '($1$3$4=="debfocalmain"){$3="jammy" ;print}' /etc/apt/sources.list \
+		> /etc/apt/sources.list.d/jammy.list
+	cat <<-EOF /etc/apt/preferences.d/libssl3
+		Package: libssl3
+		Pin: release n=jammy
+		Pin-Priority: 900
+	EOF
+	cat <<-EOF > /etc/apt/preferences.d/libssl-dev
+		Package: libssl-dev
+		Pin: release n=jammy
+		Pin-Priority: 900
+	EOF
+fi
+
+apt-get update
+apt-get install --assume-yes --no-install-recommends \
+	libsqlite3-dev \
+	libsqlite3-dev:"$1" \
+	libssl3:"$1" \
+	libssl-dev:"$1"